Remove dependency on six (#8650)

Fixes https://github.com/certbot/certbot/issues/8494.

I left the `six` dependency pinned in `tests/letstest/requirements.txt` and `tools/oldest_constraints.txt` because `six` is still a transitive dependency with our current pinnings.

The extra moving around of imports is due to me using `isort` to help me keep dependencies in sorted order after replacing imports of `six`.

* remove some six usage in acme

* remove six from acme

* remove six.add_metaclass usage

* fix six.moves.zip

* fix six.moves.builtins.open

* six.moves server fixes

* 's/six\.moves\.range/range/g'

* stop using six.moves.xrange

* fix urllib imports

* s/six\.binary_type/bytes/g

* s/six\.string_types/str/g

* 's/six\.text_type/str/g'

* fix six.iteritems usage

* fix itervalues usage

* switch from six.StringIO to io.StringIO

* remove six imports

* misc fixes

* stop using six.reload_module

* no six.PY2

* rip out six

* keep six pinned in oldest constraints

* fix log_test.py

* update changelog

4 files changed, 4 insertions, 5 deletions

diff --git a/certbot-ci/certbot_integration_tests/utils/misc.py b/certbot-ci/certbot_integration_tests/utils/misc.py
index 799b079fe..e6b9f0c88 100644
--- a/certbot-ci/certbot_integration_tests/utils/misc.py
+++ b/certbot-ci/certbot_integration_tests/utils/misc.py
@@ -4,10 +4,12 @@ or outside during setup/teardown of the integration tests environment.
 """
 import contextlib
 import errno
+import http.server as SimpleHTTPServer
 import multiprocessing
 import os
 import re
 import shutil
+import socketserver
 import stat
 import sys
 import tempfile
@@ -23,8 +25,6 @@ from cryptography.x509 import load_pem_x509_certificate
 from OpenSSL import crypto
 import pkg_resources
 import requests
-from six.moves import SimpleHTTPServer
-from six.moves import socketserver
 
 from certbot_integration_tests.utils.constants import \
      PEBBLE_ALTERNATE_ROOTS, PEBBLE_MANAGEMENT_URL
diff --git a/certbot-ci/certbot_integration_tests/utils/pebble_ocsp_server.py b/certbot-ci/certbot_integration_tests/utils/pebble_ocsp_server.py
index b86e1cbc9..4db72998f 100755
--- a/certbot-ci/certbot_integration_tests/utils/pebble_ocsp_server.py
+++ b/certbot-ci/certbot_integration_tests/utils/pebble_ocsp_server.py
@@ -4,6 +4,7 @@ This runnable module interfaces itself with the Pebble management interface in o
 to serve a mock OCSP responder during integration tests against Pebble.
 """
 import datetime
+import http.server as BaseHTTPServer
 import re
 
 from cryptography import x509
@@ -13,7 +14,6 @@ from cryptography.hazmat.primitives import serialization
 from cryptography.x509 import ocsp
 from dateutil import parser
 import requests
-from six.moves import BaseHTTPServer
 
 from certbot_integration_tests.utils.constants import MOCK_OCSP_SERVER_PORT
 from certbot_integration_tests.utils.constants import PEBBLE_MANAGEMENT_URL
diff --git a/certbot-ci/certbot_integration_tests/utils/proxy.py b/certbot-ci/certbot_integration_tests/utils/proxy.py
index 225f98e6e..7c46e640d 100644
--- a/certbot-ci/certbot_integration_tests/utils/proxy.py
+++ b/certbot-ci/certbot_integration_tests/utils/proxy.py
@@ -1,12 +1,12 @@
 #!/usr/bin/env python
 # pylint: disable=missing-module-docstring
 
+import http.server as BaseHTTPServer
 import json
 import re
 import sys
 
 import requests
-from six.moves import BaseHTTPServer
 
 from certbot_integration_tests.utils.misc import GracefulTCPServer
 
diff --git a/certbot-ci/setup.py b/certbot-ci/setup.py
index 3277df1c0..9f9c1f462 100644
--- a/certbot-ci/setup.py
+++ b/certbot-ci/setup.py
@@ -18,7 +18,6 @@ install_requires = [
     'python-dateutil',
     'pyyaml',
     'requests',
-    'six'
 ]
 
 # Add pywin32 on Windows platforms to handle low-level system calls.