tests: Remove no longer used conftest files

All the fixtures declared in them are not used anymore in the
tests of the listers ported to the new Lister API.

swh/lister/github/tests/conftest.py

@@ -1,26 +0,0 @@
-# Copyright (C) 2019-2020 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
-
-import pytest
-
-
-@pytest.fixture
-def lister_under_test():
-    return "github"
-
-
-@pytest.fixture
-def lister_github(swh_lister):
-    for task_type in [
-        {
-            "type": "load-git",
-            "description": "Load git repository",
-            "backend_name": "swh.loader.git.tasks.UpdateGitRepository",
-            "default_interval": "1 day",
-        },
-    ]:
-        swh_lister.scheduler.create_task_type(task_type)
-
-    return swh_lister