Delete dart2js specific private library code

tool/input_sdk/patch/core_patch.dart

 // 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.
 
 // Patch file for dart:core classes.
 import "dart:_internal" as _symbol_dev;
 import 'dart:_interceptors';
 import 'dart:_js_helper' show patch,
                               checkInt,
                               getRuntimeType,
                               jsonEncodeNative,
                               JSSyntaxRegExp,
                               Primitives,
                               stringJoinUnchecked,
                               objectHashCode;
 
 import 'dart:_foreign_helper' show JS;
 
 String _symbolToString(Symbol symbol) => _symbol_dev.Symbol.getName(symbol);
 
 _symbolMapToStringMap(Map<Symbol, dynamic> map) {
   if (map == null) return null;
   var result = new Map<String, dynamic>();
   map.forEach((Symbol key, value) {
     result[_symbolToString(key)] = value;
   });
   return result;
 }
 
-class SupportJsExtensionMethods {
-  const SupportJsExtensionMethods();
-}
-
 @patch
 int identityHashCode(Object object) => objectHashCode(object);
 
 // Patch for Object implementation.
 @patch
 class Object {
   @patch
   int get hashCode => Primitives.objectHashCode(this);
 
 
@@ skipping 422 matching lines @@
   @patch
   static bool get _isWindows => false;
 
   @patch
   static Uri get base {
     String uri = Primitives.currentUri();
     if (uri != null) return Uri.parse(uri);
     throw new UnsupportedError("'Uri.base' is not supported");
   }
 }