Update or delete language tests using obsolete interfaces or default factory

tests/language/is_operator_test.dart

Index: tests/language/is_operator_test.dart
===================================================================
--- tests/language/is_operator_test.dart	(revision 15648)
+++ tests/language/is_operator_test.dart	(working copy)
@@ -1,11 +1,11 @@
-// 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.
 // Dart test program for the "is" type test operator.
 
-interface I { }
+abstract class I { }
 
-interface AI extends I { }
+abstract class AI implements I { }
 
 class A implements AI {
   const A();