Remove files that have already been ported or do not need to be ported.

client/html/src/Notification.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.
-
-interface Notification extends EventTarget {
-
-  String get dir();
-
-  void set dir(String value);
-
-  EventListener get onclick();
-
-  void set onclick(EventListener value);
-
-  EventListener get onclose();
-
-  void set onclose(EventListener value);
-
-  EventListener get ondisplay();
-
-  void set ondisplay(EventListener value);
-
-  EventListener get onerror();
-
-  void set onerror(EventListener value);
-
-  String get replaceId();
-
-  void set replaceId(String value);
-
-  void cancel();
-
-  void show();
-}