Core/Misc: Do not use singleton when calling to static function ChooseDisplayId (and remove unused parameter)

src/server/game/AI/SmartScripts/SmartScriptMgr.cpp

@@ -101,8 +101,6 @@ SmartWaypointMgr::~SmartWaypointMgr()
 
         delete itr->second;
     }
-
-    waypoint_map.clear();
 }
 
 void SmartAIMgr::LoadSmartAIFromDB()