Revert of [builtins] Introduce proper Float64Exp operator.

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 2478e3fe5a23b650c40052ac290c08b02280b625..a56d325ac38b5b3de4d646241e42b7d56212a35c 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -372,9 +372,6 @@
   const Operator* Float64Atan();
   const Operator* Float64Atan2();
 
-  // Floating point exponential functions.
-  const Operator* Float64Exp();
-
   // Floating point logarithm (double-precision).
   const Operator* Float64Log();
   const Operator* Float64Log1p();