Further removal of the use of custom list class;
this time with the package lists.
Relates To #15534
Change-Id: I1f01ed9d5ddbd7754097ce0adbf505d6ba17fd2f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3732
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>