Removing unneeded from __future__ import statements.

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

ebook_converter/ebooks/pdf/pdftohtml.py

@@ -1,9 +1,3 @@
-#!/usr/bin/env python2
-# vim:fileencoding=utf-8
-# License: GPLv3 Copyright: 2008, Kovid Goyal <kovid at kovidgoyal.net>
-
-from __future__ import print_function, unicode_literals
-
 import errno
 import os
 import re