etc: remove leftover leading empty comments, blank lines

Remove leftover empty leading comments/blank lines that had been
spacers between $FreeBSD$ and the following content in config files
in src/etc.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D41548

(cherry picked from commit 9d6049d5da8ce70b3f815431bdedcee9c04f60cc)