Sync with 3.3.5a core

src/server/game/Scripting/ScriptSystem.h

@@ -52,11 +52,7 @@ class SystemMgr
         ~SystemMgr() { }
 
     public:
-        static SystemMgr* instance()
-        {
-            static SystemMgr instance;
-            return &instance;
-        }
+        static SystemMgr* instance();
 
         typedef std::unordered_map<uint32, ScriptPointVector> PointMoveMap;