config.good_job.preserve_job_records = false not working with CRON

[ollym]

When good_job runs a cron job its preserved in state finished even though we have preserve_job_records = false

[bensheldon]

This is intentional. Cron uses a unique index on (cron_key, cron_at) columns. That requires keeping the record around, otherwise it's possible that multiple jobs could be enqueued if the record is immediately deleted after running.

It's not ideal, but necessary for how cron currently works.

There's more detail in #767 / #731