Remove a lot of dead code from AXNodeObject

Source/core/accessibility/AXObject.cpp

 /*
  * Copyright (C) 2008, 2009, 2011 Apple 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 377 matching lines @@
 
     const AtomicString& result = getAttribute(aria_checkedAttr);
     if (equalIgnoringCase(result, "true"))
         return ButtonStateOn;
     if (equalIgnoringCase(result, "mixed"))
         return ButtonStateMixed;
 
     return ButtonStateOff;
 }
 
-const AtomicString& AXObject::placeholderValue() const
-{
-    const AtomicString& placeholder = getAttribute(placeholderAttr);
-    if (!placeholder.isEmpty())
-        return placeholder;
-
-    return nullAtom;
-}
-
 bool AXObject::ariaIsMultiline() const
 {
     return equalIgnoringCase(getAttribute(aria_multilineAttr), "true");
 }
 
 bool AXObject::ariaPressedIsPresent() const
 {
     return !getAttribute(aria_pressedAttr).isEmpty();
 }
 
@@ skipping 500 matching lines @@
         return ToggleButtonRole;
     if (ariaHasPopup())
         return PopUpButtonRole;
     // We don't contemplate RadioButtonRole, as it depends on the input
     // type.
 
     return ButtonRole;
 }
 
 } // namespace WebCore