[x86] Remove obsolete and unused GetBuiltinFunction.

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index a436a548e09d78c1976e3a138c0a7eebbb10f0a6..04788362c3e95571caea12d1e8927b6ad823afe8 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -331,9 +331,6 @@ class MacroAssembler: public Assembler {
                       const ParameterCount& actual, InvokeFlag flag,
                       const CallWrapper& call_wrapper);
 
-  // Store the function for the given builtin in the target register.
-  void GetBuiltinFunction(Register target, int native_context_index);
-
   // Expression support
   // cvtsi2sd instruction only writes to the low 64-bit of dst register, which
   // hinders register renaming and makes dependence chains longer. So we use