sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Add tarfs, a filesystem backed by tarballs.

Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.
Reviewed by: pauamma, imp
Differential Revision: https://reviews.freebsd.org/D37753