Raft topology goes over all nodes in a 'left' state and triggers 'remove
node' notification in case id/ip mapping is available (meaning the node
left recently), but the problem is that, since the mapping is not removed
immediately, when multiple nodes are removed in succession a notification
for the same node can be sent several times. Fix that by sending
notification only if the node still exists in the peers table. It will
be removed by the first notification and following notification will not
be sent.
Closesscylladb/scylladb#27743
