Revert of Fix clobbered register when setting this_function variable.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 64c56e2e07b2c4e93fe077f2f4f67c3d3942960c..ed29faf4ed424d5fa0898ae2a8f48fdc47b3a5a7 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -235,10 +235,6 @@
   Variable* this_function_var = scope()->this_function_var();
   if (this_function_var != nullptr) {
     Comment cmnt(masm_, "[ This function");
-    if (!function_in_register) {
-      __ movp(rdi, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
-      function_in_register = true;
-    }
     SetVar(this_function_var, rdi, rbx, rdx);
   }