|This function is PROTECTED, and can only be called from Blizzard code.
Cancels the spell awaiting target selection.
Also cancels some types of weapon buffs when they ask for confirmation. For example, if you attempt to apply a poison to a weapon that already has a poison, the game will ask you to confirm the replacement. You can accept the replacement with ReplaceEnchant() or cancel the replacement with SpellStopTargeting().