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

tools/dom/doc/html.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.
-
-// Fake dart:html library for documentation.
-
-/// The Dart HTML5 Library.
-library dart.html;
-
-part 'interface/AbstractWorker.dartdoc';
-part 'interface/Element.dartdoc';
-part 'interface/Event.dartdoc';
-part 'interface/EventTarget.dartdoc';
-part 'interface/HttpRequest.dartdoc';
-part 'interface/MouseEvent.dartdoc';
-part 'interface/Storage.dartdoc';
-part 'interface/Node.dartdoc';
-part 'interface/UIEvent.dartdoc';
-part 'interface/WebSocket.dartdoc';
-
-// Implementation files that appear to be necessary to load the sources.
-
-//part 'nodoc-src/SomeFile.dart';
-
-// Global definitions.
-
-/**
- * The top-level Window object.
- */
-Window get window() => null;
-
-/**
- * The top-level Document object.
- */
-Document get document() => null;
-
-typedef void EventListener(Event event);