sidekiq out, solid_queue in

[amatsuda]

Reasons:

1. Pure Ruby, no C extension dependencies (possibly reduces memory fragmentation issues)
2. One less service to manage (no Redis needed for jobs)
3. Currently BulkFinalizeJob is the only usage of Active Job, and since the job is very rarely executed, the inserted records will be very few. It won't bloat up the Heroku database row count.