Consider removing --restart-threshold from "aurora job restart"

We have removed restart_threshold from the updater (AURORA-479, AURORA-1252, AURORA-1254) but it's still a valid option of the "aurora job restart". It's now causing similar end user issues (interrupted restarts due to low default value of 60 seconds) and results in inconsistent user expectations.

Consider removing this option as it does not deliver much value and uses the old and now defunct restart_threshold + watch_secs formula for watching instance health.