Retinue anti-spam filter, removal of old retinue disabler system

Tested for stability.  Gave it about 40 game-years.

Not yet tested my own ability to hire, as player, the right retinues, but the logic clearly works from the observe mode total view of which AI dukes and other more-powerful-than-previously rulers have retinues.

Old maintenance events and buildings are gone for the retinue disabler, since this relies solely on the recent possibility of using proper retinue hire triggers.  Retinue caps will actually be consistent now, and now only those AI that actually would deserve a retinue in any sense or for which it makes any strategic sense to hire them (insofar as they're used in practice) will do so.

Confirmed the realm_size numbers in filter are on target via observe mode.  The independent case could go down to 12 or even 9 (from 15), but this was aesthetically pleasing.

Biggest change in the filter logic one will notice is that AI counts, for simplicity, just plain can't hire retinues anymore.  No more counting their count titles and allowing an exception if they have 2 or more.  Not only is this practically every count in PB+SWMH and usually PB, to a lesser extent, the AI is just wasting money and doesn't know what to do with these retinues at that level.  That's why they were covering the map with 250s, some 500s, and fewer 750s on almost every province.

The problem solved by this PR was not PB's fault (250- vs 500-man retinue subunits) but the LoR DLC's in general, IMHO.  Retinues are not appropriate for most rulers in the Middle Ages, especially low-level vassals that can barely afford them and will never use them.  If the LoR patch had included AI logic to use these retinues actively and only buy them if it has a need for them, it would be another thing.  This PR gives PB a reason for users to play with LoR enabled and get much more plausible results than any other mod.