Move JSSyntaxRegExp to core as a private member. This removes the last refrences to dart:coreimpl.

tests/corelib/queue_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("QueueTest.dart");
-#import("dart:coreimpl");
 
 class QueueTest {
 
   static testMain() {
     Queue queue = new Queue();
     checkQueue(queue, 0, 0);
 
     queue.addFirst(1);
     checkQueue(queue, 1, 1);
 
@@ skipping 161 matching lines @@
       entry1 = entry1.nextEntry();
       entry2 = entry2.nextEntry();
     }
     Expect.equals(null, entry2);
   }
 }
 
 main() {
   QueueTest.testMain();
 }