In order to remove them from that list, they will need to be properly removed from the TeamRaiser before removing them as a constituent.  If they have already been removed from the database, you will need to add them to a reactivation group and have support submit the task to reactivate the group.

Once this is done and the records are active again, you can use the link below to properly unregister them.

How do I unregister a TeamRaiser participant?