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: I3dadeaa3242d0b55ba891a8eb4abb199a8d2468b

designateclient/functionaltests/v2/fixtures.py

@@ -13,8 +13,6 @@ WITHOUT 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 __future__ import print_function
 import sys
 import tempfile
 import traceback

doc/examples/recordset_create.py

@@ -1,4 +1,3 @@
-from __future__ import print_function
 import logging
 import os
 

doc/examples/zone_create_primary.py

@@ -1,4 +1,3 @@
-from __future__ import print_function
 
 import logging
 import os

doc/examples/zone_list_paging.py

@@ -1,4 +1,3 @@
-from __future__ import print_function
 import logging
 import os