Scripts/Spell: fix Mixology value bonus

based on http://forum.serevo.it/index.php/topic,11211.0/wap2.html researches

maybe there is a better solution ... let me know :)

Closes  #2172
Never delete from spell_script_names by spellId if all you are doing is inserting a new script (delete by ScriptName). A single spell can have multiple scripts attached (might not be the case for these but still)