lister.github.utils: Drop no longer used module

This got detected when working on the deployment of the new loader-git.

Refs. swh/infra/sysadm-environment#5017

swh/lister/github/utils.py

-# Copyright (C) 2020-2022  The Software Heritage developers
-# See the AUTHORS file at the top-level directory of this distribution
-# License: GNU General Public License version 3, or any later version
-# See top-level LICENSE file for more information
-
-from swh.core.github.utils import *  # noqa