Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/Text.dartdoc

-// Copyright (c) 2011, 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 Text
-interface Text extends CharacterData default _TextFactoryProvider {
-
-  Text(String data);
-
-  /** @domName Text.wholeText */
-  final String wholeText;
-
-  /** @domName Text.replaceWholeText */
-  Text replaceWholeText(String content);
-
-  /** @domName Text.splitText */
-  Text splitText(int offset);
-}