They will remove themselves from that folder once they are cleared off of all systems.... there is a column called "detected", if you sort by that, you should NOT see any with Zero.
If you do, you might need to run the Gather Historical Data tool, but even without, it will self clear in time.
Do NOT delete patch content from here, if you do, you are deleting it from your core! If a system came online and needed that patch after you deleted it, it would not detect, or remediate. (It would re-download when you download content)
Thank you very much. You have answered questions for me before, I appreciate it!