Remove Salmon and PubSubHubbub (#11205)

* Remove Salmon and PubSubHubbub endpoints

* Add error when trying to follow OStatus accounts

* Fix new accounts not being created in ResolveAccountService

config/sidekiq.yml

@@ -9,9 +9,6 @@
   scheduled_statuses_scheduler:
     every: '5m'
     class: Scheduler::ScheduledStatusesScheduler
-  subscriptions_scheduler:
-    cron: '<%= Random.rand(0..59) %> <%= Random.rand(4..6) %> * * *'
-    class: Scheduler::SubscriptionsScheduler
   media_cleanup_scheduler:
     cron: '<%= Random.rand(0..59) %> <%= Random.rand(3..5) %> * * *'
     class: Scheduler::MediaCleanupScheduler