Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/CharacterData.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 CharacterData
-interface CharacterData extends Node {
-
-  /** @domName CharacterData.data */
-  String data;
-
-  /** @domName CharacterData.length */
-  final int length;
-
-  /** @domName CharacterData.appendData */
-  void appendData(String data);
-
-  /** @domName CharacterData.deleteData */
-  void deleteData(int offset, int length);
-
-  /** @domName CharacterData.insertData */
-  void insertData(int offset, String data);
-
-  /** @domName CharacterData.replaceData */
-  void replaceData(int offset, int length, String data);
-
-  /** @domName CharacterData.substringData */
-  String substringData(int offset, int length);
-}