Remove references to timed(8)

There are still references to timed(8) and timedc(8) in the base system,
which were removed in 2018.

PR: 255425
Reported by: Ceri Davies <ceri at submonkey dot net>
Reviewed by: ygy, gbe
Differential Revision: https://reviews.freebsd.org/D30232

(cherry picked from commit 1760799b4c612b98c0e5c1abeb03814e24c33cf6)