Remove recruits and soldiers from worker statistics

[GunChleoc]

https://wl.widelands.org/forum/topic/2786/?page=15#post-23858

In trunk, the statistic which shows the number of workers per time has become a little bit useless, because probably now recruits count as workers. (And every warehouse contains 100 recruits, so...) It would make more sense if recruits wouldn't be part of the statistic, like carriers and carrier animals. Wishlist: Think about removing soldiers from this statistic, too.

[GunChleoc (gunchleoc)]

Migrated to https://github.com/widelands/widelands/issues/2098