freebsd: remove __FBSDID macro use
With FreeBSD's switch to git the $FreeBSD$ string is no longer expanded
and they have mostly been removed upstream. Stop using __FBSDID and
remove the no-longer needed sys/cdefs.h includes.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Brooks Davis <brooks.davis@sri.com>
Closes #15527