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

tests/standalone/black_listed_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.
 // Dart test checking that static/instance field shadowing do not conflict.
 
 // Test that certain interfaces/classes are blacklisted from being
 // implemented or extended (VM corelib only).
 
 #library("BlackListedTest.dart");
-#import("dart:coreimpl");
 
 class MyBool extends Bool {}  /// 01: compile-time error
 
 class MyDouble extends Double {}  /// 02: compile-time error
 
 class MyObjectArray extends ObjectArray {}  /// 03: compile-time error
 
 class MyImmutableArray extends ImmutableArray {}  /// 04: compile-time error
 
 class MyGrowableObjectArray extends GrowableObjectArray {}  /// 05: compile-time error
@@ skipping 30 matching lines @@
   new MyMint(); /// 08: continued
 
   new MyBigint(); /// 09: continued
 
   new MyOneByteString(); /// 10: continued
 
   new MyTwoByteString(); /// 11: continued
 
   new MyFourByteString(); /// 12: continued
 }