Remove stale files from lib/html/src.

lib/html/src/XMLHttpRequestUploadWrappingImplementation.dart

-// Copyright (c) 2011, 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.
-
-class XMLHttpRequestUploadEventsImplementation extends EventsImplementation
-    implements XMLHttpRequestUploadEvents {
-  XMLHttpRequestUploadEventsImplementation._wrap(_ptr) : super._wrap(_ptr);
-
-  EventListenerList get abort() => _get('abort');
-  EventListenerList get error() => _get('error');
-  EventListenerList get load() => _get('load');
-  EventListenerList get loadStart() => _get('loadstart');
-  EventListenerList get progress() => _get('progress');
-}
-
-class XMLHttpRequestUploadWrappingImplementation extends EventTargetWrappingImplementation implements XMLHttpRequestUpload {
-  XMLHttpRequestUploadWrappingImplementation._wrap(ptr) : super._wrap(ptr) {}
-
-  XMLHttpRequestUploadEvents get on() {
-    if (_on === null) {
-      _on = new XMLHttpRequestUploadEventsImplementation._wrap(_ptr);
-    }
-    return _on;
-  }
-}