STPNodes are required to be discovered even though they are not monitored.
The reason they are required is to create the network/cable connections. (see emc175517)
So if you did not discover STPNodes, it would impact in network/cable connection
The default setting for stpnode monitoring is /IP/smarts/rules/devstat/sys-setting.asl default EnableSTPMonitoring = FALSE
Setting EnableSTPMonitoring to FALSE, will ensure STPNodes are not monitored and to delete the STPNodes, we can use dmctl invoke delete operation on them.
Setting STPTreeEnabled set to FALSE will disable creating the STP tree