main/rng-tools: remove start-stop-daemon's '--wait 5'
On very slow system, rngd might not have had the time to start and create its pidfile in 5 milliseconds.
We could make the delay longer, but rngd has no reason to fail spuriously so that wait does not add much value; the service will just show as crashed if it did not start properly.
follow-up of !44045 (comment 291402)