[crankshaft] Remove the useless HMapEnumLength instruction.

src/crankshaft/arm64/lithium-codegen-arm64.cc

Index: src/crankshaft/arm64/lithium-codegen-arm64.cc
diff --git a/src/crankshaft/arm64/lithium-codegen-arm64.cc b/src/crankshaft/arm64/lithium-codegen-arm64.cc
index c215e0fa92ac953dfbee7c947238234c6b7f61e6..c938dac9a875ed7998433a35867d03acf9f90839 100644
--- a/src/crankshaft/arm64/lithium-codegen-arm64.cc
+++ b/src/crankshaft/arm64/lithium-codegen-arm64.cc
@@ -3405,13 +3405,6 @@ void LCodeGen::DoLoadRoot(LLoadRoot* instr) {
 }
 
 
-void LCodeGen::DoMapEnumLength(LMapEnumLength* instr) {
-  Register result = ToRegister(instr->result());
-  Register map = ToRegister(instr->value());
-  __ EnumLengthSmi(result, map);
-}
-
-
 void LCodeGen::DoMathAbs(LMathAbs* instr) {
   Representation r = instr->hydrogen()->value()->representation();
   if (r.IsDouble()) {