Release v19.76.1

Removing a namespace failed with "Observer ... is subscribed or active and cannot be removed": the subscriptions between event stores re-subscribe the forwarding observers of every listed namespace once a minute, so an observer was subscribed again between being unsubscribed and removed. Found removing a test organization from production.

Fixed

• RemoveNamespace stops listing the namespace before removing its observers, and unsubscribes and removes an observer again, up to five times, if a subscription already on its way subscribed it in between (#4942).