Remove broken sibling selector optimization

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index 0d986e44d7d8a6b6a9ac6c37642cdd840460c96e..8cb623ba268feb004385378cc59e96ff55498649 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -183,13 +183,7 @@ public:
     void popParentShadowRoot(const ShadowRoot*);
 
     PassRefPtr<RenderStyle> styleForElement(Element*, RenderStyle* parentStyle = 0, StyleSharingBehavior = AllowStyleSharing,
-        RuleMatchingBehavior = MatchAllRules, RenderRegion* regionForStyling = 0, int childIndex = 0);
-
-    // childIndex's origin is 1, and avoids unnecessary tree walks to resolve nth/nth-last selectors.
-    PassRefPtr<RenderStyle> styleForElement(Element* element, int childIndex)
-    {
-        return styleForElement(element, 0, AllowStyleSharing, MatchAllRules, 0, childIndex);
-    }
+        RuleMatchingBehavior = MatchAllRules, RenderRegion* regionForStyling = 0);
 
     void keyframeStylesForAnimation(Element*, const RenderStyle*, KeyframeList&);