Run 2to3 -f future . -w

This will remove imports from __future__ that are no longer needed.

https://docs.python.org/3.5/library/2to3.html#2to3fixer-future

cms/envs/devstack_optimized.py

@@ -18,7 +18,7 @@ as they are for non-optimized devstack. Instead, update_assets must be
 invoked each time that changes have been made.
 """
 
-from __future__ import absolute_import
+
 
 import os