Removing unneeded from __future__ import statements.

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

ebook_converter/utils/filenames.py

@@ -1,9 +1,7 @@
-from __future__ import absolute_import, division, print_function, unicode_literals
-'''
+"""
 Make strings safe for use as ASCII filenames, while trying to preserve as much
 meaning as possible.
-'''
-
+"""
 import errno
 import os
 import shutil