fix: do not try to audit machine which no longer has `MachineStatus`

[Unix4ever]

It won't work for such machines, so treat their etcd member ID as orphaned.

This fix mitigates the following issue:

• The cluster has 3 controlplanes running.
• Controlplane A is added and joined etcd, now the cluster has 4 members.
• Controlplane A is removed ungracefully by removing it's Link.
• Before MachineSetEtcdAudit controller removes controlplane A member controlplane B is added and removed ungracefully by removing it's Link.

Before the fix, after these operations the cluster would get stuck in scaling down state due to controllers deadlock:

• MachineSetStatus controller waits for the etcd member A to be removed.
• MachineSetEtcdAudit controller tries to reach controlplane B which will never be available because it's MachineStatus no longer exist.

[Unix4ever]

/m