Change replays to store the type ID of recruits, rather than an index into the set
of possible recruits.

Negative consequences:
* Changing a type id can break replays (but how often does this happen?).

Positive consequences:
* Different parts of the code no longer need to be kept in sync to use the same
  set of recruits when calculating/using an index (c.f. r56195 and r56196).
* The code is simpler (other than the legacy support added to replay.cpp allowing
  older replays to still be replayed).


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56202 75b3775d-3801-0410-9e12-e2e43121521d