It depends how they are done.
If they are standard "Living world" vehicles, just with custom models, it should be enough to lower the Airport traffic density slider.
If they are static vehicles inserted as Simobjects, they will be removed automatic around your parking by GSX.
If they are fully custom models with custom animations playing in the scenery, there's no way to remove them unless the developer has provided with an option to do so. What you can do from GSX's side, is to change the starting position for GSX vehicles, so they might be less likely to conflict with the others.
