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

sdk/lib/coreimpl/coreimpl.dart

Index: sdk/lib/coreimpl/coreimpl.dart
diff --git a/sdk/lib/coreimpl/coreimpl.dart b/sdk/lib/coreimpl/coreimpl.dart
deleted file mode 100644
index 067ea2fe3dd668ef47b4c870d1569db4c8a0cbf7..0000000000000000000000000000000000000000
--- a/sdk/lib/coreimpl/coreimpl.dart
+++ /dev/null
@@ -1,9 +0,0 @@
-// Copyright (c) 2012, 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("dart:coreimpl");
-
-#import("dart:collection");
-
-#source("regexp.dart");