I received this information from iTunes Store/Mac App Store Customer Support:
To hide or show items on your Purchased page, follow the instructions in these articles:
iTunes Store: Hiding and unhiding purchases
Mac App Store: Hiding and unhiding purchases
You can also delete purchased content from your iTunes library or computer. This article shows you how:
Deleting files from the iTunes library and your computer
Please note that purchased content remains a part of your account's purchase history even if you hide it on your Purchased page or delete it from your computer.