Remove stale files from lib/html/src.

lib/html/src/DeviceMotionEvent.dart

Index: lib/html/src/DeviceMotionEvent.dart
diff --git a/lib/html/src/DeviceMotionEvent.dart b/lib/html/src/DeviceMotionEvent.dart
deleted file mode 100644
index 46fa55fa885ccf88d36e5134824b91ce2b551b3f..0000000000000000000000000000000000000000
--- a/lib/html/src/DeviceMotionEvent.dart
+++ /dev/null
@@ -1,12 +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 DeviceMotionEvent extends Event default DeviceMotionEventWrappingImplementation {
-
-  // TODO(nweiz): Add more arguments to the constructor when we support
-  // DeviceMotionEvent more thoroughly.
-  DeviceMotionEvent(String type, [bool canBubble, bool cancelable]);
-
-  num get interval();
-}