Revert "Gozag: only duplicate one of a stack of items."

Being able to duplicate multiple items makes the ability
much more useful; in particular, it presents the player with
a choice of using it to duplicate early-game consumables, or
wait to see if later, more valuable items show up.

TODO: figure out how to reword the description of the ability
in ^.

This reverts commit fe8694ce61bd93657398bfb710cbb022ca7a0c9d.