Remove PrivateUsers=yes from paccache.service
src/paccache.service.in:
As PrivateUsers=yes
sets up a separate namespace (also for root), all
files are therefore owned by nobody
to the paccache script and it is
not able to remove any files.
See PrivateUsers=
in
https://man.archlinux.org/man/systemd.exec.5#SANDBOXING for further
details.