Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/MutationRecord.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 MutationRecord
-interface MutationRecord {
-
-  /** @domName MutationRecord.addedNodes */
-  final NodeList addedNodes;
-
-  /** @domName MutationRecord.attributeName */
-  final String attributeName;
-
-  /** @domName MutationRecord.attributeNamespace */
-  final String attributeNamespace;
-
-  /** @domName MutationRecord.nextSibling */
-  final Node nextSibling;
-
-  /** @domName MutationRecord.oldValue */
-  final String oldValue;
-
-  /** @domName MutationRecord.previousSibling */
-  final Node previousSibling;
-
-  /** @domName MutationRecord.removedNodes */
-  final NodeList removedNodes;
-
-  /** @domName MutationRecord.target */
-  final Node target;
-
-  /** @domName MutationRecord.type */
-  final String type;
-}