Called when this system stops running because no entities match the system's EntityQuery objects or because you change the system ComponentSystemBase.Enabled property to false.
If the EntityQuery objects defined for a system do not match any existing entities then the system skips updating until a successful match is found. Likewise, if you set ComponentSystemBase.Enabled to false, then the system stops running. In both cases, OnStopRunning is called when a running system stops updating; ComponentSystemBase.OnStartRunning is called when it starts updating again.