As explained many times, the rear stairs is commonly used in real life for the cleaning crew. Maybe not as common in the US, but it's very common around the world so, GSX defaults to creating one, and let users the ability to disabled it.
Of course, like everything else in the GSX customization editor, you can apply a setting to many parking spots at once, no need to do every parking.
So, just click the button that select all parking spots with a jetway, click "Disable stairs", Apply, and that airport is done.