Revert change r12912 due to x64 perf issue

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 5439028904f429da28083e5c324707da256d5a9b..79ce9689994f76b463284623f89137d9cfba0560 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -1371,14 +1371,6 @@ class LLoadKeyed: public LTemplateInstruction<1, 2, 0> {
 };
 
 
-template <class T>
-inline static bool ArrayOpClobbersKey(T *value) {
-  CHECK(value->IsLoadKeyed() || value->IsStoreKeyed());
-  return !value->IsConstant() && (value->key()->representation().IsTagged()
-                                  || value->IsDehoisted());
-}
-
-
 class LLoadKeyedGeneric: public LTemplateInstruction<1, 2, 0> {
  public:
   LLoadKeyedGeneric(LOperand* obj, LOperand* key) {