Remove workaround for turning off authorized_keys writes
We are currently placing a workaround in the unicorn container that disables authorized_keys writes by using a rails runner and disabling it in the database.
When we are able, we should remove this workaround, either by using a new method for setting it from the config: https://gitlab.com/gitlab-org/gitlab-ee/issues/4156 or by managing the database entry through a different container (some sort of deploy or management container, one that doesn't need to be replicated and scaled like the unicorn containers)