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/opf.py

@@ -1,16 +1,13 @@
-#!/usr/bin/env python2
-# vim:fileencoding=utf-8
-from __future__ import absolute_import, division, print_function, unicode_literals
-
-__license__ = 'GPL v3'
-__copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
-
 from lxml import etree
 
 from ebook_converter.ebooks.oeb.polish.container import OPF_NAMESPACES
 from ebook_converter.utils.localization import canonicalize_lang
 
 
+__license__ = 'GPL v3'
+__copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
+
+
 def get_book_language(container):
     for lang in container.opf_xpath('//dc:language'):
         raw = lang.text