Debian cleanup: homeworld-rkt/debian/preinst: Use default path for rkt
Debian cleanup: homeworld-rkt/debian/preinst: Use default path for rkt

While we’re here, fix shellcheck warnings too.

Signed-off-by: Anders Kaseorg <087231934ba8fcf78bc142ce37d193b895ac03c4@mit.edu>

sipb/homeworld,sipb/homeworld,sipb/homeworld,sipb/homeworld