Update or delete language tests using obsolete interfaces or default factory

tests/language/factory4_test.dart

-// 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 Link<T> default LinkFactory {
-  Link.create();
+abstract class Link<T> {
+  factory Link.create() = LinkFactory.create;
 }
 
 class A<T> { }
 
 class LinkFactory<T> extends A<T> {
-  factory Link.create() {
+  factory LinkFactory.create() {
     return null;
   }
 }
 
 main() {
   var a = new Link<int>.create();
 }