PackageKit: Remove hard coded first boot package processing scripts.

Once change 2342 is in place (running first boot scripts exported from
packages), see https://review.haiku-os.org/c/haiku/+/2342,
remove data/system/boot/post_install/add_catalog_entry_attributes.sh
and related support infrastructure (magic files, launch_roster entries).

The work this script did can in fact be done at image creation time
instead of at first boot.

Change-Id: I485e1a0a87c3e6a6ba3f882e65996f2327134d37
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3751
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>