blocklist: blacklist: Chase recent upstream changes

Upstream introduced a fix that avoids blocklistd(8) from running into an
endless loop when it tries to delete an address from the database which
has been added multiple times.

Apply the same fix to blacklistd(8).

Approved by: re (cperciva)
Upstream PR: https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=57193
MFC after: 2 days

(cherry picked from commit b502a451cbae6a85636c7b8375f5ee53caca4388)
(cherry picked from commit 528e1d14037af30003b4451ec6f1686ea674621f)