Remove stale files from lib/html/src.

lib/html/src/BeforeLoadEvent.dart

Index: lib/html/src/BeforeLoadEvent.dart
diff --git a/lib/html/src/BeforeLoadEvent.dart b/lib/html/src/BeforeLoadEvent.dart
deleted file mode 100644
index 141d8e3950f7fd01b38a34c0f79d714a172f318d..0000000000000000000000000000000000000000
--- a/lib/html/src/BeforeLoadEvent.dart
+++ /dev/null
@@ -1,10 +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 BeforeLoadEvent extends Event default BeforeLoadEventWrappingImplementation {
-
-  BeforeLoadEvent(String type, String url, [bool canBubble, bool cancelable]);
-
-  String get url();
-}