[runtime] Remove the redundant %_IsObject intrinsic.

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
diff --git a/src/x64/lithium-codegen-x64.h b/src/x64/lithium-codegen-x64.h
index 2c605c2009c1677eb1c9bb24d0836af042be57ea..e05b310dec23ae9be373460c363fbc3819578f0d 100644
--- a/src/x64/lithium-codegen-x64.h
+++ b/src/x64/lithium-codegen-x64.h
@@ -265,13 +265,6 @@ class LCodeGen: public LCodeGenBase {
   // true and false label should be made, to optimize fallthrough.
   Condition EmitTypeofIs(LTypeofIsAndBranch* instr, Register input);
 
-  // Emits optimized code for %_IsObject(x).  Preserves input register.
-  // Returns the condition on which a final split to
-  // true and false label should be made, to optimize fallthrough.
-  Condition EmitIsObject(Register input,
-                         Label* is_not_object,
-                         Label* is_object);
-
   // Emits optimized code for %_IsString(x).  Preserves input register.
   // Returns the condition on which a final split to
   // true and false label should be made, to optimize fallthrough.