Removing unneeded from __future__ import statements.

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

ebook_converter/ebooks/rtf2xml/check_encoding.py

@@ -1,6 +1,3 @@
-#!/usr/bin/env python2
-from __future__ import absolute_import, division, print_function, unicode_literals
-
 import sys
 
 from ebook_converter.polyglot.builtins import unicode_type