Remove the unused HElementsKind instruction.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 5c3fd709800fbfdab1eb25c18ee8a54f6a3d56c5..b5f7f54dc8ef52b63466efe6c5e6a27770cc0223 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -1606,12 +1606,6 @@ LInstruction* LChunkBuilder::DoMapEnumLength(HMapEnumLength* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoElementsKind(HElementsKind* instr) {
-  LOperand* object = UseRegisterAtStart(instr->value());
-  return DefineAsRegister(new(zone()) LElementsKind(object));
-}
-
-
 LInstruction* LChunkBuilder::DoValueOf(HValueOf* instr) {
   LOperand* object = UseRegister(instr->value());
   LValueOf* result = new(zone()) LValueOf(object);