Removing unneeded from __future__ import statements.

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

ebook_converter/ebooks/metadata/rtf.py

@@ -1,11 +1,6 @@
-#!/usr/bin/env python2
-# vim:fileencoding=utf-8
-# License: GPLv3 Copyright: 2008, Kovid Goyal <kovid at kovidgoyal.net>
-
 """
 Edit metadata in RTF files.
 """
-from __future__ import absolute_import, division, print_function, unicode_literals
 import codecs
 import re