Ensure orderly cluster node removal on node delete via UI

When a NiFi cluster node is deleted (via the UI), a series of steps is executed to update the cluster state. If the node is being deleted due to node process failure, then any attempt to communicate with that node will fail, causing an exception.

In `NodeClusterCoordinator.removeNode()`, the sequence of steps could be improved to perform the deletion before the node participants are notified. This reduces the chance that node failure will prevent the UI operation from completing.