Revert "Parts must start with 'part of'" and "Attempt to fix VM build"

dart/tests/language/library_prefixes_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.
 
-library LibraryPrefixesTest;
-import "library_prefixes.lib";
+#library("LibraryPrefixesTest.dart");
+#import("library_prefixes.lib");
 
 class LibraryPrefixesTest {
   static testMain() {
     LibraryPrefixes.main((a, b) { Expect.equals(a, b); });
   }
 }
 
 main() {
   LibraryPrefixesTest.testMain();
 }