Remove woraround for nsm forwarding and mixins, fix has landed in SDK. (#108)

diff --git a/packages/file/CHANGELOG.md b/packages/file/CHANGELOG.md
index 733bdf3..17ee189 100644
--- a/packages/file/CHANGELOG.md
+++ b/packages/file/CHANGELOG.md
@@ -1,5 +1,7 @@
 #### dev
 
+* Update SDK constraint to 2.0.0-dev.67.0, remove workaround in 
+  recording_proxy_mixin.dart.
 * Fix usage within Dart 2 runtime mode in Dart 2.0.0-dev.61.0 and later.
 
 #### 5.0.3
diff --git a/packages/file/lib/src/backends/record_replay/recording_proxy_mixin.dart b/packages/file/lib/src/backends/record_replay/recording_proxy_mixin.dart
index 52fd9db..b95d5ed 100644
--- a/packages/file/lib/src/backends/record_replay/recording_proxy_mixin.dart
+++ b/packages/file/lib/src/backends/record_replay/recording_proxy_mixin.dart
@@ -194,25 +194,4 @@
     }
     return result;
   }
-
-  // These four abstract methods, [delete], [deleteSync], [typeSync], and
-  // [watch], are implemented by [noSuchMethod], but their presence here works
-  // around https://github.com/dart-lang/sdk/issues/33459, allowing these
-  // methods to be called within a Dart 2 runtime.
-  // TODO(srawlins): Remove these when the minimum SDK version in
-  // `pubspec.yaml` contains a fix for
-  // https://github.com/dart-lang/sdk/issues/33459.
-
-  @override
-  Future<FileSystemEntity> delete({bool recursive: false});
-
-  @override
-  void deleteSync({bool recursive: false});
-
-  @override
-  FileSystemEntityType typeSync(String path, {bool followLinks: true});
-
-  @override
-  Stream<FileSystemEvent> watch(
-      {int events: FileSystemEvent.all, bool recursive: false});
 }
diff --git a/packages/file/pubspec.yaml b/packages/file/pubspec.yaml
index 663ec19..9542f74 100644
--- a/packages/file/pubspec.yaml
+++ b/packages/file/pubspec.yaml
@@ -1,5 +1,5 @@
 name: file
-version: 5.0.3
+version: 5.0.4-dev
 authors:
 - Matan Lurey <matanl@google.com>
 - Yegor Jbanov <yjbanov@google.com>
@@ -17,4 +17,4 @@
   file_testing: '>=2.0.0 <3.0.0'
 
 environment:
-  sdk: '>=2.0.0-dev.54.0 <3.0.0'
+  sdk: '>=2.0.0-dev.67.0 <3.0.0'