The onceoff job was backported to stable in this commit:
https://github.com/discourse/discourse/commit/cf60ae32ea8c6b9a898cf64ea9d82970e26e38dd
However, the UploadRecovery.new.recover_user_profile_backgrounds method did not exist at this point, see this file:
So I guess I should manually run the onceoff job now that 2.2.1 is installed. How can I do that and is it safe?