test_listing: flake8 check

Signed-off-by: Adam Williamson <awilliam@redhat.com>

test/test_listing.py

 import unittest
 import pytest
-import logging
-import requests
-import responses
-import json
 import mwclient
 from mwclient.listing import List, GeneratorList
 
@@ -201,5 +197,6 @@ class TestList(unittest.TestCase):
         assert type(vals[1]) == mwclient.image.Image
         assert type(vals[2]) == mwclient.listing.Category
 
+
 if __name__ == '__main__':
     unittest.main()