If a DN starts decommissioning or maintenance, but goes dead before it completes the process, then the node is moved back to a state of IN_SERVICE and DEAD by the decommission monitor when it notices it has become dead. This is because decommission should gracefully remove the node, but it goes dead first, we may not be able to replicate its containers. In this case decommission effectively fails.
HDDS-5153, we decided that if a node is already dead and you decommission it, it should immediately move to DECOMMISSIONED. However that is not really consistent with the above behaviour.
Also, there is no real value in decommissioning a dead node - it does not do anything except adjust its state in SCM.
To keep things consistent, I propose we revert
HDDS-5153 so starting decommission on a dead node will work the same as when a node goes dead part way through decommission. In both cases the node will end up as IN_SERVICE + DEAD.