openssh: blocklist: Remove non async-signal safe probe

BLOCKLIST_NOTIFY() is called within a signal handler for the alarm after
the grace period has expired that may only take async-signal safe
actions.

Reviewed by: emaste
Fixes: e02003bce726 ("openssh: blocklist: Use NetBSD probes")
MFC after: 1 day
Differential Revision: https://reviews.freebsd.org/D53109