Have Sidekiq log to stdout by default.
Have Sidekiq log to stdout by default.

All of our logs need to go to stdout/stderr when running on k8s.

As of Sidekiq 6.0, the `logfile` directive and `-L` option are being
removed and logs will always go to stdout anyway:
https://github.com/mperham/sidekiq/wiki/Logging#log-redirection

Same change as alphagov/publisher@5547a1a.

SIDEKIQ_LOGFILE defaults to `log/sidekiq.log`; see
alphagov/govuk-puppet#11673.

alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2