Eliminate explicit abstract from class members in tests

tests/language/abstract_syntax_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.
 
 main() {
   var b = new B();
   Expect.equals(42, b.foo());
 }
 
 class A {
-  abstract foo();
-  abstract static bar(); /// 01: compile-time error
-  static abstract baz(); /// 02: compile-time error
+  /* abstract */ foo();
+  /* abstract */ static bar(); /// 01: compile-time error
 }
 
 class B extends A {
   foo() => 42;
   bar() => 87;
-  baz() => 99;
 }