Remove stale files from lib/html/src.

lib/html/src/TransitionEvent.dart

Index: lib/html/src/TransitionEvent.dart
diff --git a/lib/html/src/TransitionEvent.dart b/lib/html/src/TransitionEvent.dart
deleted file mode 100644
index 54c78947d4c0f937dba5f72938c96487f37fafbd..0000000000000000000000000000000000000000
--- a/lib/html/src/TransitionEvent.dart
+++ /dev/null
@@ -1,13 +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 TransitionEvent extends Event default TransitionEventWrappingImplementation {
-
-  TransitionEvent(String type, String propertyName, double elapsedTime,
-      [bool canBubble, bool cancelable]);
-
-  num get elapsedTime();
-
-  String get propertyName();
-}