Eliminate explicit abstract from class members in tests

tests/language/interface_test.dart

 // 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 testing Interfaces.
 
 interface Ai {
   int foo();
 }
 
 interface Bi extends Ai default InterfaceTest {
@@ skipping 12 matching lines @@
 
 interface Baz extends Bar, Foo { }
 
 class InterfaceTest implements Ai, Aai, Abi, Baz, Bi {
   var f;
 
   InterfaceTest() {}
   int foo() { return 1; }
 
   // intentionally unimplemented methods
-  abstract beta();
-  abstract String beta1();
-  abstract String beta2(double d);
+  beta();  // Abstract.
+  String beta1();  // Abstract.
+  String beta2(double d);  // Abstract.
 }
 
 main() {
   // instantiate an abstract class
   var o = new Bi(); /// 00: static type warning
 }