Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/OptGroupElement.dartdoc

Index: lib/html/doc/interface/OptGroupElement.dartdoc
diff --git a/lib/html/doc/interface/OptGroupElement.dartdoc b/lib/html/doc/interface/OptGroupElement.dartdoc
deleted file mode 100644
index 3fe53978b67fdbf3faf77f6bbecc56d03ac56f4c..0000000000000000000000000000000000000000
--- a/lib/html/doc/interface/OptGroupElement.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 HTMLOptGroupElement
-interface OptGroupElement extends Element default _Elements {
-
-  OptGroupElement();
-
-  /** @domName HTMLOptGroupElement.disabled */
-  bool disabled;
-
-  /** @domName HTMLOptGroupElement.label */
-  String label;
-}