Drop unnecessary RadioNodeList::m_onlyMatchImgElements member

Source/core/html/RadioNodeList.h

 /*
  * Copyright (c) 2012 Motorola Mobility, 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 33 matching lines @@
 
     String value() const;
     void setValue(const String&);
 
 private:
     RadioNodeList(ContainerNode&, const AtomicString& name, CollectionType);
 
     bool checkElementMatchesRadioNodeListFilter(const Element&) const;
 
     bool matchesByIdOrName(const Element&) const;
+    bool shouldOnlyMatchImgElements() const { return type() == RadioImgNodeListType; }
 
     virtual bool elementMatches(const Element&) const OVERRIDE;
 
     AtomicString m_name;
-    const bool m_onlyMatchImgElements;
 };
 
 } // namespace
 
 #endif