AHBot related fixes

Fix rebuild command requiring a dummy value

Fix ahbot config to normal

Fix sellprice setting in core. Closes #13425
DB/Misc: Short John Mithril / Arena Treasure Chest

* Remove permament spawn of Arena Treasure Chest 
* Script Short John Mithril to start wp at start of event, say his 2 lines (1st zone wide) and summon Arena Treasure Chest
Merge pull request #13440 from Rochet2/ahbot

Core/AH: AHBot related fixes