Removing unneeded from __future__ import statements.

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

ebook_converter/ebooks/conversion/plugins/mobi_output.py

@@ -1,15 +1,12 @@
-#!/usr/bin/env python2
-# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import absolute_import, division, print_function, unicode_literals
+from ebook_converter.customize.conversion import (OutputFormatPlugin,
+        OptionRecommendation)
+from ebook_converter.polyglot.builtins import unicode_type
+
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
 __docformat__ = 'restructuredtext en'
 
-from ebook_converter.customize.conversion import (OutputFormatPlugin,
-        OptionRecommendation)
-from ebook_converter.polyglot.builtins import unicode_type
-
 
 def remove_html_cover(oeb, log):
     from ebook_converter.ebooks.oeb.base import OEB_DOCS