Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/MessagePort.dartdoc

-// 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:
-//   This file contains documentation that is merged into the real source.
-//   Do not make code changes here.
-
-/// @domName MessagePort
-interface MessagePort extends EventTarget {
-
-  /**
-   * @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent
-   */
-  MessagePortEvents get on();
-
-  /** @domName MessagePort.addEventListener */
-  void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);
-
-  /** @domName MessagePort.close */
-  void close();
-
-  /** @domName MessagePort.dispatchEvent */
-  bool $dom_dispatchEvent(Event evt);
-
-  /** @domName MessagePort.postMessage */
-  void postMessage(String message, [List messagePorts]);
-
-  /** @domName MessagePort.removeEventListener */
-  void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]);
-
-  /** @domName MessagePort.start */
-  void start();
-
-  /** @domName MessagePort.webkitPostMessage */
-  void webkitPostMessage(String message, [List transfer]);
-}
-
-interface MessagePortEvents extends Events {
-
-  EventListenerList get message();
-}