[crankshaft] Remove the useless HMapEnumLength instruction.

src/crankshaft/x64/lithium-codegen-x64.cc

Index: src/crankshaft/x64/lithium-codegen-x64.cc
diff --git a/src/crankshaft/x64/lithium-codegen-x64.cc b/src/crankshaft/x64/lithium-codegen-x64.cc
index d4304e5405f881480ca5d038e2a66ac60f12d99d..eeed6fa6c2a88f585afc2a1fcb401e3089acef53 100644
--- a/src/crankshaft/x64/lithium-codegen-x64.cc
+++ b/src/crankshaft/x64/lithium-codegen-x64.cc
@@ -1660,13 +1660,6 @@ void LCodeGen::DoConstantT(LConstantT* instr) {
 }
 
 
-void LCodeGen::DoMapEnumLength(LMapEnumLength* instr) {
-  Register result = ToRegister(instr->result());
-  Register map = ToRegister(instr->value());
-  __ EnumLength(result, map);
-}
-
-
 Operand LCodeGen::BuildSeqStringOperand(Register string,
                                         LOperand* index,
                                         String::Encoding encoding) {