Remove stale files from lib/html/src.

lib/html/src/TextEventWrappingImplementation.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 TextEventWrappingImplementation extends UIEventWrappingImplementation implements TextEvent {
-  TextEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
-
-  factory TextEventWrappingImplementation(String type, Window view, String data,
-      [bool canBubble = true, bool cancelable = true]) {
-    final e = dom.document.createEvent("TextEvent");
-    e.initTextEvent(type, canBubble, cancelable, LevelDom.unwrap(view), data);
-    return LevelDom.wrapTextEvent(e);
-  }
-
-  String get data() => _ptr.data;
-}