_frida: Fix refcounting in get_max_argument_count()

PyTuple_GetItem() returns a borrowed reference.

Kudos to @rev1si0n for finding this embarrassing bug.

src/_frida.c

@@ -5567,8 +5567,6 @@ PyFrida_get_max_argument_count (PyObject * callable)
   Py_DECREF (is_method);
 
 beach:
-  Py_XDECREF (args);
-  Py_XDECREF (varargs);
   Py_XDECREF (spec);
 
   return result;