[Admin] Code prettification and bugfixing (#3250)

* Facelift for Admin

* Remove unnecessary converter, reorder existing steps

* Delete admin.py

* Delete __init__.py

* Delete test_admin.py

* Remove one extra unneeded check

* Create 3250.bugfix.1.rst

* Create 3250.bugfix.2.rst

* Create 3250.bugfix.3.rst

* Create 3250.bugfix.4.rst

* Create 3250.misc.1.rst

* Create 3250.misc.2.rst

* Create 3250.misc.3.rst

* Create 3250.breaking.1.rst

* Create 3250.breaking.2.rst

* ...

* I hate black...

redbot/pytest/admin.py

@@ -1,20 +0,0 @@
-from unittest.mock import MagicMock
-
-import pytest
-
-from redbot.cogs.admin import Admin
-from redbot.cogs.admin.announcer import Announcer
-
-__all__ = ["admin", "announcer"]
-
-
-@pytest.fixture()
-def admin(config):
-    return Admin(config)
-
-
-@pytest.fixture()
-def announcer(admin):
-    a = Announcer(MagicMock(), "Some message", admin.conf)
-    yield a
-    a.cancel()