[XPlane] Model set must not contain ACF models

Discussion: see https://discordapp.com/channels/539048679160676382/539064750055751690/648974956306366499

src/blackmisc/simulation/aircraftmodellist.h

@@ -340,6 +340,9 @@ namespace BlackMisc
             //! \return number of elements removed
             int removeIfExcluded();
 
+            //! Remove the XPlane flyable planes
+            int removeXPlaneFlyablePlanes();
+
             //! Remove by distributor
             //! \return number of elements removed
             int removeByDistributor(const CDistributor &distributor);