Deactivate MapQuest routing.

As of 2013-07-15 (or rather in effect around 2013-12-01) MapQuest
requires an API key, and has this nice section in their terms of usage:
"You are responsible for maintaining the confidentiality of your
Credentials and for any usage or abuse of the MapQuest Services or
MapQuest Content by anyone using your Credentials."
(from http://developer.mapquest.com/web/info/terms-of-use)