Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/MessageChannel.dartdoc

Index: lib/html/doc/interface/MessageChannel.dartdoc
diff --git a/lib/html/doc/interface/MessageChannel.dartdoc b/lib/html/doc/interface/MessageChannel.dartdoc
deleted file mode 100644
index 2626ecef0e5f6ed96244d9a2f9cc251696746414..0000000000000000000000000000000000000000
--- a/lib/html/doc/interface/MessageChannel.dartdoc
+++ /dev/null
@@ -1,19 +0,0 @@
-// 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 MessageChannel
-interface MessageChannel default _MessageChannelFactoryProvider {
-
-  MessageChannel();
-
-  /** @domName MessageChannel.port1 */
-  final MessagePort port1;
-
-  /** @domName MessageChannel.port2 */
-  final MessagePort port2;
-}