software/metabase/test: stop using six

this package is python3

software/metabase/test/setup.py

@@ -45,7 +45,6 @@ setup(name=name,
         'slapos.cookbook',
         'slapos.libnetworkcache',
         'supervisor',
-        'six',
         'requests'
         ],
       zip_safe=True,

software/metabase/test/test.py

 ##############################################################################
-# coding: utf-8
 #
 # Copyright (c) 2020 Nexedi SA and Contributors. All Rights Reserved.
 #
@@ -28,7 +27,7 @@
 
 import os
 import json
-from six.moves.urllib import parse
+from urllib import parse
 import requests
 
 from slapos.testing.testcase import makeModuleSetUpAndTestCaseClass