Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/FontElement.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 HTMLFontElement
-interface FontElement extends Element {
-
-  /** @domName HTMLFontElement.color */
-  String color;
-
-  /** @domName HTMLFontElement.face */
-  String face;
-
-  /** @domName HTMLFontElement.size */
-  String size;
-}