Remove "Delete tenant" functionality

Continuation of https://github.com/oaeproject/3akai-ux/issues/3718.

The "Delete Tenant" functionality has been removed from the UI in the User Management work. The functionality should now also be removed from Hilary.
That raises an interesting point. I believe we have at least one tenant that was created and then removed from the production environment. This patch would probably cause that tenant to show back up. Should the migration tool also remove these? If so, I'm assuming there will be problems with the items that were created within that tenant.

It might be worth querying the production database to see if this is really something we have to take into account.