Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/FileWriterSync.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 FileWriterSync
-interface FileWriterSync {
-
-  /** @domName FileWriterSync.length */
-  final int length;
-
-  /** @domName FileWriterSync.position */
-  final int position;
-
-  /** @domName FileWriterSync.seek */
-  void seek(int position);
-
-  /** @domName FileWriterSync.truncate */
-  void truncate(int size);
-
-  /** @domName FileWriterSync.write */
-  void write(Blob data);
-}