Remove mock dependency (#8630)

Fixes https://github.com/certbot/certbot/issues/7913.

I only added the deprecation warning to `certbot.tests.util` because that's the only place where I think someone could be using the `mock` module through our API.

* remove external mock from acme

* update Certbot's mock usage

* remove mock dependency in plugins

* remove external mock from compatibility test

* add changelog entry

certbot-compatibility-test/certbot_compatibility_test/configurators/apache/common.py

@@ -2,11 +2,8 @@
 import os
 import shutil
 import subprocess
+from unittest import mock
 
-try:
-    import mock
-except ImportError: # pragma: no cover
-    from unittest import mock # type: ignore
 import zope.interface
 
 from certbot import errors as le_errors

certbot-compatibility-test/certbot_compatibility_test/validator_test.py

@@ -1,10 +1,7 @@
 """Tests for certbot_compatibility_test.validator."""
 import unittest
+from unittest import mock
 
-try:
-    import mock
-except ImportError: # pragma: no cover
-    from unittest import mock # type: ignore
 import OpenSSL
 import requests
 

certbot-compatibility-test/setup.py

@@ -1,7 +1,5 @@
-from distutils.version import LooseVersion
 import sys
 
-from setuptools import __version__ as setuptools_version
 from setuptools import find_packages
 from setuptools import setup
 
@@ -15,15 +13,6 @@ install_requires = [
     'zope.interface',
 ]
 
-setuptools_known_environment_markers = (LooseVersion(setuptools_version) >= LooseVersion('36.2'))
-if setuptools_known_environment_markers:
-    install_requires.append('mock ; python_version < "3.3"')
-elif 'bdist_wheel' in sys.argv[1:]:
-    raise RuntimeError('Error, you are trying to build certbot wheels using an old version '
-                       'of setuptools. Version 36.2+ of setuptools is required.')
-elif sys.version_info < (3,3):
-    install_requires.append('mock')
-
 if sys.version_info < (2, 7, 9):
     # For secure SSL connexion with Python 2.7 (InsecurePlatformWarning)
     install_requires.append('ndg-httpsclient')