Remove external mock dependency (#9331)

* Remove external mock dependency

This also removes the "external-mock" test environment

* remove superfluous ignores

* remove mock warning ignore from pytest.ini

* drop deps on mock in oldest, drop dep on types-mock

Co-authored-by: Alex Zorin <alex@zorin.id.au>

certbot-apache/tests/util.py

@@ -4,11 +4,7 @@ import unittest
 
 import augeas
 import josepy as jose
-
-try:
-    import mock
-except ImportError:  # pragma: no cover
-    from unittest import mock  # type: ignore
+from unittest import mock
 
 from certbot.compat import os
 from certbot.plugins import common