Both Recruiting MAIs: switch to using external CAs

This includes disabling the rush recruiter for the time being, as the
engine files it uses do not yet use the external CAs.  It will be
re-enabled once those have been converted as well.
Recruiting MAIs: get rid of recruiting_type= key

The previous value of recruiting_type= now goes directly into ai_type=.
 Also add syntax translation and deprecation message.