Remove outdated versions

Remove old versions and add style updates.

doc/administration/geo/replication/troubleshooting.md

@@ -678,20 +678,6 @@ sudo /opt/gitlab/embedded/bin/gitlab-pg-ctl promote
 
 GitLab 12.9 and later are [unaffected by this error](https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/5147).
 
-### Two-factor authentication is broken after a failover
-
-The setup instructions for Geo prior to 10.5 failed to replicate the
-`otp_key_base` secret, which is used to encrypt the two-factor authentication
-secrets stored in the database. If it differs between **primary** and **secondary**
-nodes, users with two-factor authentication enabled won't be able to log in
-after a failover.
-
-If you still have access to the old **primary** node, you can follow the
-instructions in the
-[Upgrading to GitLab 10.5](../replication/version_specific_updates.md#updating-to-gitlab-105)
-section to resolve the error. Otherwise, the secret is lost and you'll need to
-[reset two-factor authentication for all users](../../../security/two_factor_authentication.md#disabling-2fa-for-everyone).
-
 ## Expired artifacts
 
 If you notice for some reason there are more artifacts on the Geo