Update or delete language tests using obsolete interfaces or default factory

tests/language/class_extends_negative_test.dart

Index: tests/language/class_extends_negative_test.dart
===================================================================
--- tests/language/class_extends_negative_test.dart	(revision 15648)
+++ tests/language/class_extends_negative_test.dart	(working copy)
@@ -1,21 +0,0 @@
-// Copyright (c) 2011, 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.
-// Check fails because class extends from interface.
-
-interface InterfaceA {
-
-}
-
-class ClassA extends InterfaceA {
-
-}
-
-class ClassExtendsNegativeTest {
-  static testMain() {
-  }
-}
-
-main() {
-  ClassExtendsNegativeTest.testMain();
-}