sshd: remove unneeded initialization of libwrap logging severities

This part of ca573c9a177 proved to be unnecessary. As the removed
comment says, we set them merely for logging syntax errors, as we log
refusals ourselves. However, inside the libwrap the parser logs any
syntax errors with tcpd_warn() which has hardcoded LOG_WARNING inside.

Reviewed by: philip, emaste
Differential revision: https://reviews.freebsd.org/D40068