Remove Apple's unused implementation of private browsing from WebCore

Source/WebCore/page/Page.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 274 matching lines @@
 
     void suspendScriptedAnimations();
     void resumeScriptedAnimations();
     bool scriptedAnimationsSuspended() const { return m_scriptedAnimationsSuspended; }
 
     void userStyleSheetLocationChanged();
     const String& userStyleSheet() const;
 
     void dnsPrefetchingStateChanged();
     void storageBlockingStateChanged();
-    void privateBrowsingStateChanged();
 
     static void removeAllVisitedLinks();
 
     static void allVisitedStateChanged(PageGroup*);
     static void visitedStateChanged(PageGroup*, LinkHash visitedHash);
 
     StorageNamespace* sessionStorage(bool optionalCreate = true);
     void setSessionStorage(PassRefPtr<StorageNamespace>);
 
     void setCustomHTMLTokenizerTimeDelay(double);
@@ skipping 178 matching lines @@
 inline PageGroup& Page::group()
 {
     if (!m_group)
         initGroup();
     return *m_group;
 }
 
 } // namespace WebCore
     
 #endif // Page_h