style: remove unused imports

cubicweb_s3storage/storages.py

@@ -21,7 +21,6 @@
 import uuid
 from logging import getLogger
 
-from six import PY3
 import os
 import boto3
 

test/test_s3storage.py

@@ -2,8 +2,6 @@
 from contextlib import contextmanager
 from unittest.mock import patch
 
-from six import PY3
-
 from cubicweb.server.sources import storages
 from cubicweb.devtools.testlib import CubicWebTC
 from cubicweb import Binary