There is no way to remove www or control how your URL will show up in your ads. It used to be that you could but not anymore, for almost two years now in fact and is a sore point with many advertisers. Google claims that having the www in front and the domain all in lower case increases the click rate. I and others question this. It may be done just so ads look more like the SERPs and thus blurring the distinction between ads and organics.