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

client/html/src/MessagePort.dart

Index: client/html/src/MessagePort.dart
diff --git a/client/html/src/MessagePort.dart b/client/html/src/MessagePort.dart
deleted file mode 100644
index a270e0b396fd47e8ce458633f4772caaae952b57..0000000000000000000000000000000000000000
--- a/client/html/src/MessagePort.dart
+++ /dev/null
@@ -1,6 +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 MessagePort extends EventTarget {
-}