HOW-TO: Hide Previously Installed Apps in the App Store
As many have found you cannot currently delete apps that you have installed in the past, but you CAN hide them.
Follow these instructions:
1) Open App store
2) Click Updates at bottom right
3) either click ALL or Not on this Phone
4) Find the App you want to hide
5) Swipe your finger over the app you want to hide to the LEFT
6) Click Hide
iPhone 4, iOS 5