games/luanti: move from games/minetest, update 5.9.1 → 5.10.0

Upstream now installs compatibility symlinks minetest→luanti and
minetestserver→luantiserver. UIDs/GIDs, rc.d script, runtime
directories, config file, rc.conf variables related to the port
were not changed (just the manpages were renamed), so systemwide
minetestserver should not require any changes to keep running.