Remove generated directories with 100s of files.

client/dom/generated/src/wrapping/_MessageChannelWrappingImplementation.dart

-// 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.
-
-// WARNING: Do not edit - generated code.
-
-class _MessageChannelWrappingImplementation extends DOMWrapperBase implements MessageChannel {
-  _MessageChannelWrappingImplementation() : super() {}
-
-  static create__MessageChannelWrappingImplementation() native {
-    return new _MessageChannelWrappingImplementation();
-  }
-
-  MessagePort get port1() { return _get_port1(this); }
-  static MessagePort _get_port1(var _this) native;
-
-  MessagePort get port2() { return _get_port2(this); }
-  static MessagePort _get_port2(var _this) native;
-
-  String get typeName() { return "MessageChannel"; }
-}