gh-160147: Optimize make_new_set_untracked() (#161191)

There is no need to set PySetObject explicitly to 0/NULL, since
_PyType_AllocNoTrack() already initialize memory to zeros.

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>

Author: vstinner

Objects/setobject.c

@@ -1348,19 +1348,20 @@ static PyObject *
 make_new_set_untracked(PyTypeObject *type, PyObject *iterable)
 {
     assert(PyType_Check(type));
-    PySetObject *so;
 
-    so = (PySetObject *)_PyType_AllocNoTrack(type, 0);
-    if (so == NULL)
+    // fields are zero-initialized by _PyType_AllocNoTrack
+    PySetObject *so = (PySetObject *)_PyType_AllocNoTrack(type, 0);
+    if (so == NULL) {
         return NULL;
+    }
 
-    so->fill = 0;
-    so->used = 0;
+    assert(so->fill == 0);
+    assert(so->used == 0);
     so->mask = PySet_MINSIZE - 1;
     so->table = so->smalltable;
     so->hash = -1;
-    so->finger = 0;
-    so->weakreflist = NULL;
+    assert(so->finger == 0);
+    assert(so->weakreflist == NULL);
 
     if (iterable != NULL) {
         if (set_update_local(so, iterable)) {