Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/TextTrackList.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 TextTrackList
-interface TextTrackList extends EventTarget {
-
-  /**
-   * @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent
-   */
-  TextTrackListEvents get on();
-
-  /** @domName TextTrackList.length */
-  final int length;
-
-  /** @domName TextTrackList.addEventListener */
-  void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);
-
-  /** @domName TextTrackList.dispatchEvent */
-  bool $dom_dispatchEvent(Event evt);
-
-  /** @domName TextTrackList.item */
-  TextTrack item(int index);
-
-  /** @domName TextTrackList.removeEventListener */
-  void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]);
-}
-
-interface TextTrackListEvents extends Events {
-
-  EventListenerList get addTrack();
-}