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.

Change-Id: I23bdb623c36732ac4a886ad22e8155763040dba5

searchlight/cmd/control.py

@@ -18,9 +18,6 @@ Helper script for starting/stopping/reloading Searchlight server programs.
 Thanks for some of the code, Swifties and Glance Gladiators ;)
 """
 
-from __future__ import print_function
-from __future__ import with_statement
-
 import argparse
 import fcntl
 import os

searchlight/common/wsgi.py

@@ -19,7 +19,6 @@
 """
 Utility methods for working with WSGI servers
 """
-from __future__ import print_function
 
 import errno
 import functools

tools/install_venv.py

@@ -21,8 +21,6 @@
 Installation script for SearchLight's development virtualenv
 """
 
-from __future__ import print_function
-
 import os
 import sys
 

tools/install_venv_common.py

@@ -22,8 +22,6 @@ environment, it should be kept strictly compatible with Python 2.6.
 Synced in from openstack-common
 """
 
-from __future__ import print_function
-
 import optparse
 import os
 import subprocess