pvecm status
Highest expected: 4
pvecm delnode <hostname> Killing node 2
pvecm status
Highest expected: 3
And reload WebUI to refresh cluster nodes.
ceph mon remove <host>
ceph osd out osd.2 ceph osd crush remove osd.2 ceph auth del osd.2 ceph osd rm osd.2 ceph osd crush rm <host>