That is a bug, and should have been removed. In the original game, there were cursed equipment items, and when you equipped one of these items (in the original game you could not tell what an item was until you equipped it), you were not able to un-equip it later. The 'Remove Curse' spell allowed you to remove one cursed item from a player. This was never implemented, and the spell should have been removed. I will add it to the list of things to fix in the next version.
Thanks for the report.