Remove stale files from lib/html/src.

lib/html/src/PageTransitionEvent.dart

Index: lib/html/src/PageTransitionEvent.dart
diff --git a/lib/html/src/PageTransitionEvent.dart b/lib/html/src/PageTransitionEvent.dart
deleted file mode 100644
index 2d71d3f8f5ed9943763acd17c3b30546e90b7e4c..0000000000000000000000000000000000000000
--- a/lib/html/src/PageTransitionEvent.dart
+++ /dev/null
@@ -1,11 +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.
-
-interface PageTransitionEvent extends Event default PageTransitionEventWrappingImplementation {
-
-  PageTransitionEvent(String type, [bool canBubble, bool cancelable,
-      bool persisted]);
-
-  bool get persisted();
-}