Invalid dest for message on teardown

[sed-i]

On teardown, maelstrom has an AssertionError when one of the nodes attempts to send to a node that was already torn down.
Seems like this assertion error shouldn't be happening / printed.

INFO [2023-04-13 01:55:14,033] jepsen node n2 - maelstrom.db Tearing down n2
WARN [2023-04-13 01:55:14,033] n4 stdout - maelstrom.process Error!
java.lang.AssertionError: Assert failed: Invalid dest for message #maelstrom.net.message.Message{:id 518901, :src "n4", :dest "n1", :body {:msg_id 108978, :type "broadcast", :message 36}}