Battle engine: Restore used items on retry

Due to Scott's lack of backup in the final battle, Robert is impossible
to defeat without items, so now used items are restored when "Retry
Battle" is selected.
Make Robert close out with Omni

Technically, the battle will end with a countered Charge Slash if the
player is doing it right, but it's always preceded by Omni (which is
intended to be Guarded against), so it still counts!
RSB II: Move final Holy Water before Desperation

Robert will now use Holy Water to cure his Zombie status (if needed)
before Desperation Slash instead of after, making it a bit easier to
prevent the fifth phase from happening.