Remove dead code from childIndex optimization

Source/core/css/SelectorChecker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 658 matching lines @@
                 return siblingTraversalStrategy.isFirstOfType(element, element.tagQName()) && siblingTraversalStrategy.isLastOfType(element, element.tagQName());
             }
             break;
         case CSSSelector::PseudoNthChild:
             if (!selector.parseNth())
                 break;
             if (ContainerNode* parent = element.parentElementOrShadowRoot()) {
                 int count = 1 + siblingTraversalStrategy.countElementsBefore(element);
                 if (m_mode == ResolvingStyle) {
                     RenderStyle* childStyle = context.elementStyle ? context.elementStyle : element.renderStyle();
-                    element.setChildIndex(count);
                     if (childStyle)
                         childStyle->setUnique();
                     parent->setChildrenAffectedByForwardPositionalRules();
                 }
 
                 if (selector.matchNth(count))
                     return true;
             }
             break;
         case CSSSelector::PseudoNthOfType:
@@ skipping 444 matching lines @@
     return element.focused() && isFrameFocused(element);
 }
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const DOMSiblingTraversalStrategy&, MatchResult*) const;
 
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const ShadowDOMSiblingTraversalStrategy&, MatchResult*) const;
 
 }