Revert mixin fix r41424 until mirrors issue 21474 is fixed.

tests/language/mixin_type_parameter6_test.dart

Index: tests/language/mixin_type_parameter6_test.dart
===================================================================
--- tests/language/mixin_type_parameter6_test.dart	(revision 41424)
+++ tests/language/mixin_type_parameter6_test.dart	(working copy)
@@ -1,17 +0,0 @@
-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-class A<T> {}
-
-class B<S> {
-  int foo(S s) => null;
-}
-
-class C extends A<int> with B<String> {}
-
-main() {
-  var list = <String>['foo'];
-  var c = new C();
-  list.map(c.foo);
-}