Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/Clipboard.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 Clipboard
-interface Clipboard {
-
-  /** @domName Clipboard.dropEffect */
-  String dropEffect;
-
-  /** @domName Clipboard.effectAllowed */
-  String effectAllowed;
-
-  /** @domName Clipboard.files */
-  final FileList files;
-
-  /** @domName Clipboard.items */
-  final DataTransferItemList items;
-
-  /** @domName Clipboard.types */
-  final List types;
-
-  /** @domName Clipboard.clearData */
-  void clearData([String type]);
-
-  /** @domName Clipboard.getData */
-  String getData(String type);
-
-  /** @domName Clipboard.setData */
-  bool setData(String type, String data);
-
-  /** @domName Clipboard.setDragImage */
-  void setDragImage(ImageElement image, int x, int y);
-}