PKGBUILD: use upstream default config(s)

The logrotate.conf shipped with this package has been unchanged since 2013, despite the upstream config(s) it was derived from receiving multiple changes since then. The original reason for not shipping the upstream default, adding .pac{orig,new,save} to the taboo extension list, has been adressed with 66c191fa861965748e1868a7c4454660e50c4da2, so there is no longer a reason to keep the maintenance burden around.