include: ssp: kill off leftover $FreeBSD$ tag

Most of these were fixed when rebasing the patch forward, but this one
seems to have been missed.

Reported by: marck
Fixes: be04fec426 ("Import _FORTIFY_SOURCE implementation [...]")

Import _FORTIFY_SOURCE implementation from NetBSD

This is a mostly-unmodified copy of the various *_chk implementations
and headers from NetBSD, without yet modifying system headers to start
actually including them. A future commit will also apply the needed
bits to fix ssp/unistd.h.

Reviewed by: imp, pauamma_gundo.com (both previous versions), kib
Sponsored by: Stormshield
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D32306