Remove unused SmiTryAddConstant from X64 macro assembler

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 646d7fafc0a575f81ef93f42741512883893de91..8c73dd92b332f8d69088d40da2c1e800267ab5f2 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -532,15 +532,6 @@ class MacroAssembler: public Assembler {
   // Smis represent a subset of integers. The subset is always equivalent to
   // a two's complement interpretation of a fixed number of bits.
 
-  // Optimistically adds an integer constant to a supposed smi.
-  // If the src is not a smi, or the result is not a smi, jump to
-  // the label.
-  void SmiTryAddConstant(Register dst,
-                         Register src,
-                         Smi* constant,
-                         Label* on_not_smi_result,
-                         Label::Distance near_jump = Label::kFar);
-
   // Add an integer constant to a tagged smi, giving a tagged smi as result.
   // No overflow testing on the result is done.
   void SmiAddConstant(Register dst, Register src, Smi* constant);