Remove $FreeBSD$: one-line sh pattern

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

Move sysctl.conf to sbin/sysctl/ and switch to CONFS.

This helps with pkgbase to tag this config file as a config file.

Approved by: allanjude (mentor), will (mentor)
Differential Revision: https://reviews.freebsd.org/D16559