Remove "from __future__ import print"

This was well-intentioned, but it causes more trouble
than it's worth.

Fixes #652

examples/numberedports.py

@@ -6,7 +6,6 @@ Validate that the port numbers match to the interface name,
 and that the ovs ports match the mininet ports.
 """
 
-from __future__ import print_function
 
 from mininet.net import Mininet
 from mininet.node import Controller