Remove usage of six

The repo is python 3 only now, we can remove six usage and assume
python3 everywhere.

Change-Id: I0c742c2c7898914fae48b675e53c4dafb358bf9a

hacking/checks/except_checks.py

@@ -15,8 +15,6 @@
 import ast
 import re
 
-from six import PY2
-
 from hacking import core
 
 RE_ASSERT_RAISES_EXCEPTION = re.compile(r"self\.assertRaises\(Exception[,\)]")
@@ -61,13 +59,7 @@ def hacking_except_format_assert(logical_line, noqa):
 
 
 def is_none(node):
-    '''Check whether an AST node corresponds to None.
-
-    In Python 2 None uses the same ast.Name class that variables etc. use,
-    but in Python 3 there is a new ast.NameConstant class.
-    '''
-    if PY2:
-        return isinstance(node, ast.Name) and node.id == 'None'
+    '''Check whether an AST node corresponds to None.'''
     return isinstance(node, ast.NameConstant) and node.value is None
 
 

hacking/config.py

@@ -11,12 +11,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from six import moves
+import configparser
 
 
 class Config(object):
     def __init__(self, default_section=None, tox_file='tox.ini'):
-        conf = moves.configparser.RawConfigParser()
+        conf = configparser.RawConfigParser()
         conf.read(tox_file)
 
         self.conf = conf

hacking/tests/test_doctest.py

@@ -20,7 +20,6 @@ import sys
 import tempfile
 
 import pkg_resources
-import six
 import testscenarios
 from testtools import content
 
@@ -75,7 +74,7 @@ def load_tests(loader, tests, pattern):
             continue
 
         check = entry.load()
-        if check.skip_on_py3 and six.PY3:
+        if check.skip_on_py3:
             continue
 
         name = entry.attrs[0]

lower-constraints.txt

@@ -22,7 +22,6 @@ pytz==2013.6
 PyYAML==3.12
 reno==2.5.0
 requests==2.14.2
-six==1.10.0
 snowballstemmer==1.2.1
 stestr==2.0.0
 testscenarios==0.4

requirements.txt

@@ -1,2 +1 @@
 flake8<4.0.0,>=3.6.0 # MIT
-six>=1.10.0 # MIT