What do you mean with "default state" ?
- Going back to the old default jetway (CTRL+J) on that airport only ? Sorry, you can't do that. Either you restore default jetways everywhere, or you replace them everywhere. The sim has only one jetway model, so there's no way around this, other than patching thousands of AFCAD individually.
- Going back to the default GSX/SODE replacement model ? This can't be easier: just press the Reset button on the parking you want to reset, or on all parking spots at once, and it will go back to default. However, your method of removing the .INI file would work just as well so, if it's "not working", perhaps you meant the first thing ?