Revert "Added support for iOS6"

This reverts commit c5d84f0a7cf7b16a589eac4836ce41db790977eb.

- performBatchUpdates:completion: does not respect that a view starts off in the visible rect in iOS6. This causes the animation to not actually have any of the zoom in animation. It does however seem to work fine for zoom out. This appears to be an issue with iOS6 collection views as this works for iOS7 and up