Remove the old hand-written HTML doc format, which has not worked for months.

tools/dom/doc/interface/EventTarget.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: Do not edit - generated code.
-
-abstract class EventListenerList {
-  EventListenerList add(EventListener handler, [bool useCapture]);
-
-  EventListenerList remove(EventListener handler, [bool useCapture]);
-
-  bool dispatch(Event evt);
-}
-
-abstract class Events {
-  EventListenerList operator [](String type);
-}
-
-/// @domName EventTarget
-abstract class EventTarget {
-
-  /** @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent */
-  abstract Events get on;
-
-  /** @domName EventTarget.addEventListener */
-  void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);
-
-  /** @domName EventTarget.dispatchEvent */
-  bool $dom_dispatchEvent(Event event);
-
-  /** @domName EventTarget.removeEventListener */
-  void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]);
-
-}