Remove $FreeBSD$: one-line sh pattern

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

daily 150.clean-hoststat: suppress error when using dma

dma(8) does not have hoststat or purgestat, so this script produces
an error from the daily script. We could disable this script, but
that would mean yet another change to switch back to sendmail. Check
for purgestat in mailer.conf before attempting either hoststat or
purgestat.

Reviewed by: pstef, bapt
Differential Revision: https://reviews.freebsd.org/D37712

Move all periodic related config and scripts to usr.sbin/periodic/

This makes pkgbase easier by tagging these as CONFS so they are properly
tagged as config files.

Approved by: will (mentor)
Sponsored by: Essen Hackathon
Differential Revision: https://reviews.freebsd.org/D16553