[x86] Remove obsolete and unused GetBuiltinFunction.

src/x87/macro-assembler-x87.h

Index: src/x87/macro-assembler-x87.h
diff --git a/src/x87/macro-assembler-x87.h b/src/x87/macro-assembler-x87.h
index f7c689a2391475abbddab62f8aaacda0024a62c6..855852b940331c2b40d75973439cb546df36696b 100644
--- a/src/x87/macro-assembler-x87.h
+++ b/src/x87/macro-assembler-x87.h
@@ -326,9 +326,6 @@ 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
   // Support for constant splitting.