Clean up WithNullSafetyMixin in analyzer/ and analyzer_plugin/.

Bug: https://github.com/dart-lang/sdk/issues/43837
Change-Id: I2282d0230e5ea0abdd2a08de2a16cfaa602c3cc8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/174223
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
diff --git a/pkg/analyzer/test/src/dart/constant/evaluation_test.dart b/pkg/analyzer/test/src/dart/constant/evaluation_test.dart
index a1753b8..30e51fb 100644
--- a/pkg/analyzer/test/src/dart/constant/evaluation_test.dart
+++ b/pkg/analyzer/test/src/dart/constant/evaluation_test.dart
@@ -1083,8 +1083,6 @@
     writeTestPackageAnalysisOptionsFile(
       AnalysisOptionsFileConfig(
         experiments: [
-          // TODO(scheglov) https://github.com/dart-lang/sdk/issues/43837
-          EnableString.non_nullable,
           EnableString.triple_shift,
         ],
       ),
diff --git a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
index 16d21b17..90337b6 100644
--- a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
+++ b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
@@ -4,14 +4,12 @@
 
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
-import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/analysis_context_collection.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/dart/analysis/driver_based_analysis_context.dart';
-import 'package:analyzer/src/dart/analysis/experiments.dart';
 import 'package:analyzer/src/generated/engine.dart' show AnalysisOptionsImpl;
 import 'package:analyzer/src/test_utilities/mock_packages.dart';
 import 'package:analyzer/src/test_utilities/mock_sdk.dart';
@@ -361,23 +359,8 @@
 
 mixin WithNullSafetyMixin on PubPackageResolutionTest {
   @override
-  String get testPackageLanguageVersion =>
-      Feature.non_nullable.isEnabledByDefault ? '2.12' : '2.11';
+  String get testPackageLanguageVersion => '2.12';
 
   @override
   bool get typeToStringWithNullability => true;
-
-  /// TODO(scheglov) https://github.com/dart-lang/sdk/issues/43837
-  /// Remove when Null Safety is enabled by default.
-  @nonVirtual
-  @override
-  void setUp() {
-    super.setUp();
-
-    writeTestPackageAnalysisOptionsFile(
-      AnalysisOptionsFileConfig(
-        experiments: [EnableString.non_nullable],
-      ),
-    );
-  }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/invalid_language_override_greater_test.dart b/pkg/analyzer/test/src/diagnostics/invalid_language_override_greater_test.dart
index 03e35bc..dd1ee88 100644
--- a/pkg/analyzer/test/src/diagnostics/invalid_language_override_greater_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/invalid_language_override_greater_test.dart
@@ -38,12 +38,12 @@
   test_greaterThanPackage() async {
     _configureTestPackageLanguageVersion('2.5');
     await assertNoErrorsInCode(r'''
-// @dart = 2.10
+// @dart = 2.12
 int? a;
 ''');
     _assertUnitLanguageVersion(
       package: Version.parse('2.5.0'),
-      override: Version.parse('2.10.0'),
+      override: Version.parse('2.12.0'),
     );
   }
 
@@ -70,18 +70,9 @@
   }
 
   void _configureTestPackageLanguageVersion(String versionStr) {
-    newFile('$testPackageRootPath/.dart_tool/package_config.json', content: '''
-{
-  "configVersion": 2,
-  "packages": [
-    {
-      "name": "test",
-      "rootUri": "../",
-      "packageUri": "lib/",
-      "languageVersion": "$versionStr"
-    }
-  ]
-}
-''');
+    writeTestPackageConfig(
+      PackageConfigFileBuilder(),
+      languageVersion: versionStr,
+    );
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/sdk_version_gt_gt_gt_operator_test.dart b/pkg/analyzer/test/src/diagnostics/sdk_version_gt_gt_gt_operator_test.dart
index 6ea9193..5f103da 100644
--- a/pkg/analyzer/test/src/diagnostics/sdk_version_gt_gt_gt_operator_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/sdk_version_gt_gt_gt_operator_test.dart
@@ -28,8 +28,6 @@
     writeTestPackageAnalysisOptionsFile(
       AnalysisOptionsFileConfig(
         experiments: [
-          // TODO(scheglov) https://github.com/dart-lang/sdk/issues/43837
-          EnableString.non_nullable,
           EnableString.triple_shift,
         ],
       ),
diff --git a/pkg/analyzer_plugin/test/support/abstract_context.dart b/pkg/analyzer_plugin/test/support/abstract_context.dart
index e2e289b..a648c3f 100644
--- a/pkg/analyzer_plugin/test/support/abstract_context.dart
+++ b/pkg/analyzer_plugin/test/support/abstract_context.dart
@@ -4,7 +4,6 @@
 
 import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/analysis_context_collection.dart';
-import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -14,7 +13,6 @@
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/dart/analysis/driver_based_analysis_context.dart';
-import 'package:analyzer/src/dart/analysis/experiments.dart';
 import 'package:analyzer/src/generated/engine.dart' show AnalysisEngine;
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/generated/testing/element_search.dart';
@@ -22,7 +20,6 @@
 import 'package:analyzer/src/test_utilities/mock_sdk.dart';
 import 'package:analyzer/src/test_utilities/package_config_file_builder.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
-import 'package:meta/meta.dart';
 
 /// Finds an [Element] with the given [name].
 Element findChildElement(Element root, String name, [ElementKind kind]) {
@@ -174,23 +171,7 @@
 
 mixin WithNullSafetyMixin on AbstractContextTest {
   @override
-  String get testPackageLanguageVersion =>
-      Feature.non_nullable.isEnabledByDefault ? '2.12' : '2.11';
-
-  bool get withPackageMeta => false;
-
-  /// TODO(scheglov) https://github.com/dart-lang/sdk/issues/43837
-  /// Remove when Null Safety is enabled by default.
-  @nonVirtual
-  @override
-  void setUp() {
-    super.setUp();
-    writeTestPackageConfig(
-      languageVersion: testPackageLanguageVersion,
-      meta: withPackageMeta,
-    );
-    createAnalysisOptionsFile(experiments: [EnableString.non_nullable]);
-  }
+  String get testPackageLanguageVersion => '2.12';
 }
 
 /// Wraps the given [_ElementVisitorFunction] into an instance of