Drop traverseNextElement() method from HTMLCollection class

Source/core/html/HTMLCollection.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Samsung Electronics. All rights reserved.
  *
  * 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.
@@ skipping 107 matching lines @@
         m_namedItemCache = cache;
     }
 
     NamedItemCache& namedItemCache() const
     {
         ASSERT(m_namedItemCache);
         return *m_namedItemCache;
     }
 
 private:
-    Element* traverseNextElement(Element& previous) const;
-
     void invalidateIdNameCacheMaps(Document* oldDocument = 0) const
     {
         if (!hasValidIdNameCache())
             return;
 
         // Make sure we decrement the NodeListWithIdNameCache count from
         // the old document instead of the new one in the case the collection
         // is moved to a new document.
         unregisterIdNameCacheFromDocument(oldDocument ? *oldDocument : document());
 
@@ skipping 18 matching lines @@
 {
     if (!attrName || shouldInvalidateTypeOnAttributeChange(invalidationType(), *attrName))
         invalidateCache();
     else if (*attrName == HTMLNames::idAttr || *attrName == HTMLNames::nameAttr)
         invalidateIdNameCacheMaps();
 }
 
 } // namespace
 
 #endif