devctl: don't publish the mount options

Mount options aren't solely ASCII strings. In addition, experience to
date suggests that the mount options are much less useful than was
originally supposed and the mount flags suffice to make decisions. Drop
the reporting of options for the mount/remount/unmount events.

Reviewed by: markj
Reported by: KASAN
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D31287