Remove explicit interface versions of dartdoc files.

lib/html/doc/interface/OptionElement.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 HTMLOptionElement
-interface OptionElement extends Element default _OptionElementFactoryProvider {
-
-  OptionElement([String data, String value, bool defaultSelected, bool selected]);
-
-  /** @domName HTMLOptionElement.defaultSelected */
-  bool defaultSelected;
-
-  /** @domName HTMLOptionElement.disabled */
-  bool disabled;
-
-  /** @domName HTMLOptionElement.form */
-  final FormElement form;
-
-  /** @domName HTMLOptionElement.index */
-  final int index;
-
-  /** @domName HTMLOptionElement.label */
-  String label;
-
-  /** @domName HTMLOptionElement.selected */
-  bool selected;
-
-  /** @domName HTMLOptionElement.value */
-  String value;
-}