Revert of [builtins] Introduce proper Float64Exp operator.

src/x64/codegen-x64.h

Index: src/x64/codegen-x64.h
diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h
index 62945f70f8bb921d8e1e9f220bcc70a1c2c0417b..1403781c67b3425aca71d4c84b6d8e623560ac02 100644
--- a/src/x64/codegen-x64.h
+++ b/src/x64/codegen-x64.h
@@ -25,6 +25,20 @@
 
  private:
   DISALLOW_COPY_AND_ASSIGN(StringCharLoadGenerator);
+};
+
+
+class MathExpGenerator : public AllStatic {
+ public:
+  static void EmitMathExp(MacroAssembler* masm,
+                          XMMRegister input,
+                          XMMRegister result,
+                          XMMRegister double_scratch,
+                          Register temp1,
+                          Register temp2);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MathExpGenerator);
 };