Remove our two borg hosts from the inventory

These are managed services and Ansible doesn't run on them. It got boring writing 'all,!rsync_net,!hetzner_storageboxes' in playbooks and ad-hoc commands, so remove these borg hosts from our inventory.

In the process to accomplish the above, I refactored the roles that set up our borg hosts to run on localhost; seems to work well and should prove more flexible if we were to get another storage box.

docs/otp.md

@@ -56,7 +56,7 @@ Run
 
     pass otp insert -i rsync.net -a archlinux Rsync.net/archlinux-master-token -s
 
-When asked for a secret, provide the `2FA token seed` from `group_vars/all/vault_rsync.net.yml`.
+When asked for a secret, provide the `2FA token seed` from `host_vars/localhost/vault_rsync.net.yml`.
 You can then run
 
     pass otp code Rsync.net/archlinux-master-token