If you close the purchase requisition then the same will not be considered in MD04 and no need to delete.
Image may be NSFW.
Clik here to view.
Could you please explain how do you proceed after do PGI against OD. I believe the process might be convert PR into PO and then GR against PO. If yes, until convert PO the PR will consider in MD04 and until post GR the PO will consider in MD04. This is standard behaviour too.