Eliminate old style import from language tests

tests/language/prefix11_negative_test.dart

 // 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.
 //
 // Symbols in libraries imported by the prefixed library should not be visible
 
-#library("Prefix11NegativeTest.dart");
-#import("library12.dart", prefix:"lib12");
+library Prefix11NegativeTest.dart;
+import "library12.dart" as lib12;
 
 main() {
   var obj = new lib12.Library11(1); // Error, method should not be visible
 }