release: Chase location of pkg repo databases

pkg used to store copies of upstream repository databases in
/var/db/pkg/repo-*.sqlite. About a year ago this was moved to
/var/db/pkg/repos/*/, resulting in FreeBSD cloud images no longer
having those (unhelpful since they'll be long out of date before
the cloud images are launched) databases removed.

Remove the correct location, and hope that future pkg updates don't
break the base system again.

Sponsored by: Amazon
Approved by: re (cperciva)

(cherry picked from commit 078e8b34b13d6d0663661542eeac9007806fccdc)
(cherry picked from commit 8984d070d6669669754ba1f66c7acd6d7dca1d2a)