bpo-36974: remove _PyObject_HasFastCall (GH-13460)

diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
index 13f2db9..213fb3e 100644
--- a/Modules/_functoolsmodule.c
+++ b/Modules/_functoolsmodule.c
@@ -107,7 +107,7 @@
         return NULL;
     }
 
-    pto->use_fastcall = _PyObject_HasFastCall(func);
+    pto->use_fastcall = (_PyVectorcall_Function(func) != NULL);
 
     return (PyObject *)pto;
 }
@@ -365,7 +365,7 @@
         Py_INCREF(dict);
 
     Py_INCREF(fn);
-    pto->use_fastcall = _PyObject_HasFastCall(fn);
+    pto->use_fastcall = (_PyVectorcall_Function(fn) != NULL);
     Py_SETREF(pto->fn, fn);
     Py_SETREF(pto->args, fnargs);
     Py_SETREF(pto->kw, kw);