MaistraDiscoveryNamespacesFilter has race

The MaistraDiscoveryNamespacesFilter introduced as part of OSSM-1420 has a race, where the namespace updates from the SMMR come in, resulting in new objects coming down the queue, but the namespace list inside the filter hasn't updated yet, so it rejects those events. The simple solution is just to not filter anything, because xns-informer already does it for us.

Note to QE: this is a regression introduced during 2.2 development and does not need verification (I have an integration test for it, too)