Geo: Improve process for removing the tracking DB during a Geo failover

The Disaster recovery documentation has the step Removing the former secondary’s tracking database, this lists the steps on how to delete the Tracking Database after promoting a secondary site. The DB needs to be removed to prevent issues if the site is ever returned to running as a secondary.

The current process is to just delete the tracking databases data directory. This only works when the database is being run as an omnibus node, if the user is using an external database the steps will be different. Ideally the process should occur automatically as part of the promotion process. If rails was responsible for removing the data then the process would work regardless of where the database was being run.

We currently run gitlab-ctl geo promote on the rails node as part of the promotion process, could the tracking DB be destroyed as part of this existing step.