You should certainly be deleting items from your queue - and how/when you do this should both adhere to the Archiving & Data policy that should be part of your Robotic Operating Model, and mentioned in your solution design.
Items are deleted using the Delete Items or Delete Item actions in the internal work queue object. The Delete Items action will delete worked items older than a set age - this should eitehr be placed at the end of your main process to maintain the queue, or some clients have a seperate work queue deleting process for all work queues that is ran daily at non-peak times.
For items that have not been worked that you want to clear down for some reason, you would first need to mark them as an exception before you can delete them. That would be a bespoke tidy up process - maybe getting the get report data action to return the items want so you can process them. There should be no unworked items in a soltuion unless something has gone very wrong (such as the infastructure has gone down and items have been worked manually) - so if that is a standard part of your solution it might be worth revisiting your design.
