Stop to use the __future__ module.

The __future__ module [1] was used in this context to ensure compatibility
between python 2 and python 3.

We previously dropped the support of python 2.7 [2] and now we only support
python 3 so we don't need to continue to use this module and the imports
listed below.

Imports commonly used and their related PEPs:
- `division` is related to PEP 238 [3]
- `print_function` is related to PEP 3105 [4]
- `unicode_literals` is related to PEP 3112 [5]
- `with_statement` is related to PEP 343 [6]
- `absolute_import` is related to PEP 328 [7]

[1] https://docs.python.org/3/library/__future__.html
[2] https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html
[3] https://www.python.org/dev/peps/pep-0238
[4] https://www.python.org/dev/peps/pep-3105
[5] https://www.python.org/dev/peps/pep-3112
[6] https://www.python.org/dev/peps/pep-0343
[7] https://www.python.org/dev/peps/pep-0328

Change-Id: Ic03754dcaaa4f1c0018294aa52bb05d956aa5d10

doc/source/conf.py

@@ -22,8 +22,6 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
-from __future__ import print_function
-
 import logging
 import os
 import sys

horizon/templatetags/bootstrap.py

@@ -13,8 +13,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import absolute_import
-
 from django import template
 
 

horizon/templatetags/horizon.py

@@ -12,8 +12,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 from collections import OrderedDict
 
 from django.conf import settings

horizon/utils/csvbase.py

@@ -10,8 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import division
-
 import csv
 import io
 

openstack_dashboard/api/cinder.py

@@ -18,8 +18,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 import logging
 import math
 

openstack_dashboard/api/glance.py

@@ -16,9 +16,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-from __future__ import division
-
 import _thread as thread
 import collections
 from collections import abc

openstack_dashboard/api/neutron.py

@@ -17,8 +17,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 import collections
 from collections.abc import Sequence
 import copy

openstack_dashboard/api/nova.py

@@ -18,8 +18,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 import collections
 import logging
 from operator import attrgetter

openstack_dashboard/management/commands/make_web_conf.py

@@ -10,8 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import print_function
-
 import multiprocessing
 import os
 import re

openstack_dashboard/management/commands/migrate_settings.py

@@ -10,8 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import print_function
-
 import difflib
 import imp
 import os

openstack_dashboard/management/commands/upgrade_check.py

@@ -10,9 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-
-from __future__ import print_function
-
 import json
 import sys
 

openstack_dashboard/templatetags/context_selection.py

@@ -12,8 +12,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 from django.conf import settings
 from django import template
 

openstack_dashboard/templatetags/themes.py

@@ -13,8 +13,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import absolute_import
-
 import os
 
 from urllib.request import pathname2url

openstack_dashboard/test/unit/api/test_base.py

@@ -16,8 +16,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 from django.conf import settings
 
 from horizon import exceptions

openstack_dashboard/test/unit/api/test_keystone.py

@@ -15,8 +15,6 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
-
-from __future__ import absolute_import
 from unittest import mock
 
 

openstack_dashboard/test/unit/api/test_nova.py

@@ -16,8 +16,6 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
-
-from __future__ import absolute_import
 from unittest import mock
 
 from django.conf import settings

openstack_dashboard/test/unit/api/test_swift.py

@@ -15,8 +15,6 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
-
-from __future__ import absolute_import
 from unittest import mock
 
 from horizon import exceptions

openstack_dashboard/test/unit/usage/test_quotas.py

@@ -17,8 +17,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from __future__ import absolute_import
-
 import collections
 from unittest import mock
 

openstack_dashboard/usage/base.py

@@ -10,8 +10,6 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-from __future__ import division
-
 import datetime
 
 from django.conf import settings

tools/policy-diff.py

@@ -12,8 +12,6 @@
 
 """Tool to check policy file differeneces."""
 
-from __future__ import print_function
-
 import argparse
 
 import yaml