[crankshaft] Remove the useless HMapEnumLength instruction.

src/crankshaft/arm64/lithium-arm64.h

Index: src/crankshaft/arm64/lithium-arm64.h
diff --git a/src/crankshaft/arm64/lithium-arm64.h b/src/crankshaft/arm64/lithium-arm64.h
index 1b627d13f85461e2c97caf500ba59a4575b4d135..4ddd3aceb57d2333be7f615eedb885cfd2ea1b75 100644
--- a/src/crankshaft/arm64/lithium-arm64.h
+++ b/src/crankshaft/arm64/lithium-arm64.h
@@ -106,7 +106,6 @@ class LCodeGen;
   V(LoadNamedField)                          \
   V(LoadNamedGeneric)                        \
   V(LoadRoot)                                \
-  V(MapEnumLength)                           \
   V(MathAbs)                                 \
   V(MathAbsTagged)                           \
   V(MathClz32)                               \
@@ -1791,18 +1790,6 @@ class LLoadRoot final : public LTemplateInstruction<1, 0, 0> {
 };
 
 
-class LMapEnumLength final : public LTemplateInstruction<1, 1, 0> {
- public:
-  explicit LMapEnumLength(LOperand* value) {
-    inputs_[0] = value;
-  }
-
-  LOperand* value() { return inputs_[0]; }
-
-  DECLARE_CONCRETE_INSTRUCTION(MapEnumLength, "map-enum-length")
-};
-
-
 template<int T>
 class LUnaryMathOperation : public LTemplateInstruction<1, 1, T> {
  public: