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/setup.py

@@ -90,7 +90,6 @@ test_extras = [
     'pytest-xdist',
     'setuptools',
     'tox',
-    'types-mock',
     'types-pyOpenSSL',
     'types-pyRFC3339',
     'types-pytz',