Don't attempt to kill() the constraint in the wrong process. The
process management of the contraint processes has been moved from ntp
to the parent, for better privsep and pledge, but the ntp process
still attempted to kill the constraints on timeout directly. Fix this
regression by introducing a new imsg from ntp to the parent and the
related logic to kill a constraint at the right place.
Reported & tested by bcook@
Ok bcook@