You can't delete them because they aren't stored in your iCloud account (and don't use any of your storage). They are stored in the iTunes store. Those are just links to your previous purchases so you can redownload them from the iTunes store if you want to. If you don't want to see these, you can go to Settings>iTunes & App Store and turn Videos off under Show All. If you want to hide them on your purchased list, hide them in iTunes on your computer as explained here: http://support.apple.com/kb/HT4919.