Update or delete language tests using obsolete interfaces or default factory

tests/language/implicit_this_test.dart

Index: tests/language/implicit_this_test.dart
===================================================================
--- tests/language/implicit_this_test.dart	(revision 15648)
+++ tests/language/implicit_this_test.dart	(working copy)
@@ -1,8 +1,8 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 
-interface Interface {
+abstract class Interface {
   final x;
 }