Remove files that have already been ported or do not need to be ported.

client/html/src/LoseContext.dart

Index: client/html/src/LoseContext.dart
diff --git a/client/html/src/LoseContext.dart b/client/html/src/LoseContext.dart
deleted file mode 100644
index e420efbe5c44f3be67ec2a758a8a27749ecfd507..0000000000000000000000000000000000000000
--- a/client/html/src/LoseContext.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 LoseContext {
-
-  void loseContext();
-
-  void restoreContext();
-}