if you want to just flat out get rid of it, use this method.
http://kc-mm.com/stickman/kcmm-tutorial-how-to-delete-parts-from-3d-models/12-22-2009/involves a fair amount of hexing, but not too bad because you can follow along with the video. and keep in mind that there are a few polygons that don't like to be deleted. you won't find that out until you get lagged in game, but that will be the cause. but since it's a face you want to remove, removing it shouldn't cause an issue.