Removing unneeded from __future__ import statements.

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

ebook_converter/library/field_metadata.py

@@ -1,11 +1,8 @@
-from __future__ import absolute_import, division, print_function, unicode_literals
-
-'''
+"""
 Created on 25 May 2010
 
 @author: charles
-'''
-
+"""
 import traceback
 from collections import OrderedDict