Remove stale files from lib/html/src.

lib/html/src/HashChangeEventWrappingImplementation.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.
-
-class HashChangeEventWrappingImplementation extends EventWrappingImplementation implements HashChangeEvent {
-  HashChangeEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
-
-  factory HashChangeEventWrappingImplementation(String type, String oldURL,
-      String newURL, [bool canBubble = true, bool cancelable = true]) {
-    final e = dom.document.createEvent("HashChangeEvent");
-    e.initHashChangeEvent(type, canBubble, cancelable, oldURL, newURL);
-    return LevelDom.wrapHashChangeEvent(e);
-  }
-
-  String get newURL() => _ptr.newURL;
-
-  String get oldURL() => _ptr.oldURL;
-}