Django 2 Upgrade (part 1): Drop Python2 support __future__ imports removal.

[noliveleger]

To avoid another huge PR, I made this seperate PR to remove all import __future__.
There is (should be) no other changes in this PR.

[jnm]

$ git diff origin/2489-remove-__future__-import origin/two-databases | grep -vE '^(\+\+\+|---) ' | grep '^[+-]' | sort | uniq
+
+                        absolute_import, division)
+from __future__ import absolute_import
+from __future__ import absolute_import, unicode_literals
+from __future__ import (division, print_function, absolute_import,
+#     from __future__ import print_function
+from __future__ import unicode_literals
+from __future__ import (unicode_literals, print_function,
+#     import requests
-#     #     import sys
+#     import sys
+import sys
+                        unicode_literals)