Remove generated directories with 100s of files.

client/dom/generated/src/interface/MessagePort.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.
-
-// WARNING: Do not edit - generated code.
-
-interface MessagePort extends EventTarget {
-
-  void addEventListener(String type, EventListener listener, [bool useCapture]);
-
-  void close();
-
-  bool dispatchEvent(Event evt);
-
-  void postMessage(String message, [List messagePorts]);
-
-  void removeEventListener(String type, EventListener listener, [bool useCapture]);
-
-  void start();
-
-  void webkitPostMessage(String message, [List transfer]);
-}