Remove TODO from Team.hpp

I thought that we wanted `Team` to behave as an iterator over its `Players`, but the implementation is [quite complicated](http://www.boost.org/doc/libs/1_55_0/libs/iterator/doc/index.html) AFAICT and it's easier to just get the player container with `get_players()` and work with that. `Team` can still store players however it wants, so we're not hurting abstraction.