Remove --supermixin flag from VM.

tests/language/mixin_super_use_test.dart

 // Copyright (c) 2013, 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.
 
 import "package:expect/expect.dart";
 
 class M {
 }
 
 class P0 {
   foo() {
-    super.toString();    /// 01: compile-time error
-    super.foo();         /// 02: compile-time error
-    super.bar = 100;     /// 03: compile-time error
+    super.toString();
 
     void inner() {
-      super.toString();  /// 04: compile-time error
-      super.foo();       /// 05: compile-time error
-      super.bar = 100;   /// 06: compile-time error
+      super.toString();
     }
     inner();
 
     (() {
-      super.toString();  /// 07: compile-time error
-      super.foo();       /// 08: compile-time error
-      super.bar = 100;   /// 09: compile-time error
+      super.toString();
     })();
 
     return 42;
   }
 }
 
 class P1 {
   bar() {
-    super.toString();    /// 10: compile-time error
+    super.toString();
     return 87;
   }
 
   // The test method is strategically placed here to try to force the
   // P1 class and its bar method to be resolved before resolving the
   // mixin applications.
   test() {
     new C();
     var d = new D();
     var e = new E();
     var f = new F();
     Expect.equals(42, d.foo());
     Expect.equals(87, e.bar());
     Expect.equals(99, f.baz());
   }
 }
 
 class P2 {
   baz() {
-    super.toString();   /// 11: compile-time error
+    super.toString();
     return 99;
   }
 }
 
 class C = Object with M;
 class D = Object with P0;
 class E = Object with M, P1;
 class F = Object with P2, M;
 
 main() {
   var p1 = new P1();
   var p2 = new P2();
   Expect.equals(87, p1.bar());
   p1.test();
   Expect.equals(99, p2.baz());
 }