[crankshaft] Remove the useless HMapEnumLength instruction.

src/crankshaft/x64/lithium-x64.cc

Index: src/crankshaft/x64/lithium-x64.cc
diff --git a/src/crankshaft/x64/lithium-x64.cc b/src/crankshaft/x64/lithium-x64.cc
index c945bca3352a60ddd4c77d75ab928a28e918e5c5..2a32900a404521b4e2612a1be2e3ca319f798390 100644
--- a/src/crankshaft/x64/lithium-x64.cc
+++ b/src/crankshaft/x64/lithium-x64.cc
@@ -1781,12 +1781,6 @@ LInstruction* LChunkBuilder::DoClassOfTestAndBranch(
 }
 
 
-LInstruction* LChunkBuilder::DoMapEnumLength(HMapEnumLength* instr) {
-  LOperand* map = UseRegisterAtStart(instr->value());
-  return DefineAsRegister(new(zone()) LMapEnumLength(map));
-}
-
-
 LInstruction* LChunkBuilder::DoSeqStringGetChar(HSeqStringGetChar* instr) {
   LOperand* string = UseRegisterAtStart(instr->string());
   LOperand* index = UseRegisterOrConstantAtStart(instr->index());