Remove stale files from lib/html/src.

lib/html/src/PopStateEventWrappingImplementation.dart

Index: lib/html/src/PopStateEventWrappingImplementation.dart
diff --git a/lib/html/src/PopStateEventWrappingImplementation.dart b/lib/html/src/PopStateEventWrappingImplementation.dart
deleted file mode 100644
index bd2f021f4f21caac446ca4d7cf04f041236826ed..0000000000000000000000000000000000000000
--- a/lib/html/src/PopStateEventWrappingImplementation.dart
+++ /dev/null
@@ -1,16 +0,0 @@
-// 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 PopStateEventWrappingImplementation extends EventWrappingImplementation implements PopStateEvent {
-  PopStateEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
-
-  factory PopStateEventWrappingImplementation(String type, Object state,
-      [bool canBubble = true, bool cancelable = true]) {
-    final e = dom.document.createEvent("PopStateEvent");
-    e.initPopStateEvent(type, canBubble, cancelable, state);
-    return LevelDom.wrapPopStateEvent(e);
-  }
-
-  String get state() => _ptr.state;
-}