Remove stale files from lib/html/src.

lib/html/src/AnimationEvent.dart

Index: lib/html/src/AnimationEvent.dart
diff --git a/lib/html/src/AnimationEvent.dart b/lib/html/src/AnimationEvent.dart
deleted file mode 100644
index 085383ac3f31e401ca9e95a8bfcf6758520f94ba..0000000000000000000000000000000000000000
--- a/lib/html/src/AnimationEvent.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 AnimationEvent extends Event default AnimationEventWrappingImplementation {
-
-  AnimationEvent(String type, String propertyName, double elapsedTime,
-      [bool canBubble, bool cancelable]);
-
-  String get animationName();
-
-  num get elapsedTime();
-}