Remove the DelayedJobs gem and database table. Completes the transition
to GoodJob started in c06bfa64f and f4953549a.
Downstream users can upgrade as follows:
* Stop the Rails server.
* Stop the DelayedJobs worker (normally running as `bin/delayed_job` or `bin/rails jobs:work`).
* Run `bin/rails jobs:work` to finish any pending delayed jobs.
* Run `bin/rails db:migrate` to create the good_jobs table and drop the delayed_jobs table.
* Start the Rails server again.
* Start the GoodJobs worker with `bin/good_job start`.
3841fba78e