eliminate reallocation of races on every serialization

Now only done once for each client from choose race view respectively
at game startup; the call was already there.
This allows simplification of the owner members in
CInGameEntity, since regetting is only neccessary at an actual change,
and owner members in the race tree will still be valid (instead of
being a pointer to an obsolete CRace object).
changes which are possible according to previous commit

-slight optimization: get owner only if it changes
-remove obsolete comment
-allow owner functionality in CRace tree

For a major race it doesn't make sense though. Unused for minor.