Remove boilerplate in _functools.

Author: ZeroIntensity

Modules/_functoolsmodule.c

@@ -108,20 +108,13 @@ placeholder_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
     return placeholder;
 }
 
-static int
-placeholder_traverse(PyObject *self, visitproc visit, void *arg)
-{
-    Py_VISIT(Py_TYPE(self));
-    return 0;
-}
-
 static PyType_Slot placeholder_type_slots[] = {
     {Py_tp_dealloc, placeholder_dealloc},
     {Py_tp_repr, placeholder_repr},
     {Py_tp_doc, (void *)placeholder_doc},
     {Py_tp_methods, placeholder_methods},
     {Py_tp_new, placeholder_new},
-    {Py_tp_traverse, placeholder_traverse},
+    {Py_tp_traverse, _PyObject_VisitType},
     {0, 0}
 };