Remove outdated ObjC-related comments from the IDL

Source/core/dom/MessagePort.idl

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 10 matching lines @@
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 
 [
     ActiveDOMObject
 ] interface MessagePort : EventTarget {
-// We need to have something as an ObjC binding, because MessagePort is used in MessageEvent, which already has one,
-// but we don't want to actually expose the API while it is in flux.
     [Custom, RaisesException] void postMessage(any message, optional Array messagePorts);
 
     void start();
     void close();
 
     // event handler attributes
     attribute EventHandler onmessage;
 };