Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/KeyboardEvent.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 KeyboardEvent
-interface KeyboardEvent extends UIEvent {
-
-  /** @domName KeyboardEvent.altGraphKey */
-  final bool altGraphKey;
-
-  /** @domName KeyboardEvent.altKey */
-  final bool altKey;
-
-  /** @domName KeyboardEvent.ctrlKey */
-  final bool ctrlKey;
-
-  /** @domName KeyboardEvent.keyIdentifier */
-  final String keyIdentifier;
-
-  /** @domName KeyboardEvent.keyLocation */
-  final int keyLocation;
-
-  /** @domName KeyboardEvent.metaKey */
-  final bool metaKey;
-
-  /** @domName KeyboardEvent.shiftKey */
-  final bool shiftKey;
-
-  /** @domName KeyboardEvent.initKeyboardEvent */
-  void initKeyboardEvent(String type, bool canBubble, bool cancelable, Window view, String keyIdentifier, int keyLocation, bool ctrlKey, bool altKey, bool shiftKey, bool metaKey, bool altGraphKey);
-}