autofs: Remove stale comment

devd action for automount -c was never commented.

Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D42493
Reviewed by: rew

(cherry picked from commit 5a78fcfce4c563fcd47dcfb6f36aff2bdd14839b)