(MCO-360) Remove all references to the 'mcollective' agent

Controller messages have been deprecated for an extremely long time.
After deprecating it we stopped processing messages directed at the
'mcollective' agent but we are still connecting to its related queues
and topics.

This commit removes all trace of the 'mcollective' agent and controller
messages.
This pair of expectations feels a little weird.  I can see how they're useful immediately to transition the code, but later I'm not sure it'll be clear the intent, even with the comment.