Revert "extension type support for `avoid_shadowing_type_parameters`" (dart-lang/linter#4691)

This reverts commit c9a082f00cc580fa6c98eefd038f14dd9192c376.
diff --git a/lib/src/rules/avoid_shadowing_type_parameters.dart b/lib/src/rules/avoid_shadowing_type_parameters.dart
index f9f7789..a8bb0f6 100644
--- a/lib/src/rules/avoid_shadowing_type_parameters.dart
+++ b/lib/src/rules/avoid_shadowing_type_parameters.dart
@@ -98,9 +98,6 @@
         _checkForShadowing(typeParameters, parent.typeParameters, 'enum');
       } else if (parent is ExtensionDeclaration) {
         _checkForShadowing(typeParameters, parent.typeParameters, 'extension');
-      } else if (parent is ExtensionTypeDeclaration) {
-        _checkForShadowing(
-            typeParameters, parent.typeParameters, 'extension type');
       } else if (parent is MethodDeclaration) {
         _checkForShadowing(typeParameters, parent.typeParameters, 'method');
       } else if (parent is MixinDeclaration) {
diff --git a/test/rules/avoid_shadowing_type_parameters_test.dart b/test/rules/avoid_shadowing_type_parameters_test.dart
index 7cf3a51..fb713ba 100644
--- a/test/rules/avoid_shadowing_type_parameters_test.dart
+++ b/test/rules/avoid_shadowing_type_parameters_test.dart
@@ -8,15 +8,13 @@
 
 main() {
   defineReflectiveSuite(() {
+    defineReflectiveTests(AvoidShadowingTypeParametersEnumTest);
     defineReflectiveTests(AvoidShadowingTypeParametersTest);
   });
 }
 
 @reflectiveTest
-class AvoidShadowingTypeParametersTest extends LintRuleTest {
-  @override
-  List<String> get experiments => ['inline-class'];
-
+class AvoidShadowingTypeParametersEnumTest extends LintRuleTest {
   @override
   String get lintRule => 'avoid_shadowing_type_parameters';
 
@@ -30,16 +28,12 @@
       lint(33, 1),
     ]);
   }
-
-  test_extensionType() async {
-    await assertDiagnostics(r'''
-extension type E<T>(int i) {
-  void m<T>() {}
 }
-''', [
-      lint(38, 1),
-    ]);
-  }
+
+@reflectiveTest
+class AvoidShadowingTypeParametersTest extends LintRuleTest {
+  @override
+  String get lintRule => 'avoid_shadowing_type_parameters';
 
   test_wrongNumberOfTypeArguments() async {
     await assertDiagnostics(r'''