blocklistd: Remove obsolete network class reference

This was a comment in a configuration example.

Reported by: bapt
Reviewed by: bapt, jlduran
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48810

(cherry picked from commit 513c4e20790a24526cb1c2f5a4725971a09d928a)