Removing unneeded from __future__ import statements.

Since we are on Python 3.6 and up, we don't need those anymore.

ebook_converter/ebooks/oeb/polish/container.py

@@ -1,8 +1,3 @@
-#!/usr/bin/env python2
-# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:fdm=marker:ai
-# License: GPLv3 Copyright: 2013, Kovid Goyal <kovid at kovidgoyal.net>
-from __future__ import absolute_import, division, print_function, unicode_literals
-
 import errno
 import hashlib
 import logging