Move database clean from cron to Sidekiq scheduler

After moving the remaining tasks from schedule.rb to sidekiq.yml, we can
remove whenever and won't rely on cron any more. That will simplify the
setup and migration to a new server.

config/schedule.rb

@@ -11,10 +11,6 @@ env "MAILTO", ENV["SCHEDULE_NOTIFICATIONS"] if ENV["SCHEDULE_NOTIFICATIONS"]
 # If we use -e with a file containing specs, rspec interprets it and filters out our examples
 job_type :run_file, "cd :path; :environment_variable=:environment bundle exec script/rails runner :task :output"
 
-every 1.month, at: '4:30am' do
-  rake 'ofn:data:remove_transient_data'
-end
-
 every 1.day, at: '2:45am' do
   rake 'db2fog:clean' if ENV['S3_BACKUPS_BUCKET']
 end

config/sidekiq.yml

@@ -19,3 +19,6 @@
       every: "5m"
     OrderCycleClosingJob:
       every: "5m"
+    RakeJob:
+      args: ["ofn:data:remove_transient_data"]
+      cron: "30 4 1 * *"