closes bpo-34504: Remove the useless NULL check in PySequence_Check(). (GH-8935)

Reported by Svace static analyzer.

Objects/abstract.c

@@ -1510,7 +1510,7 @@ PySequence_Check(PyObject *s)
 {
     if (PyDict_Check(s))
         return 0;
-    return s != NULL && s->ob_type->tp_as_sequence &&
+    return s->ob_type->tp_as_sequence &&
         s->ob_type->tp_as_sequence->sq_item != NULL;
 }