node doesn't clean up the process.targets (used for Link/Monitor) on target termination

[halturin]

Process has 'targets' field (sync.Map) where pid,name,alias,event are stored on Link/Monitor creation.
This field helps to prevent to have a link and monitor with/on target simultaneously (or to create a second Link or Monitor on the same target).

In case of target termination node sends an exit-signal or down-message but doesn't remove this target from the process.targets map.