Most of the good ol' boys making it big in country music these days wouldn't be caught dead without cowboy headgear. In fact, people like Garth Brooks, Clint Black, and Alan Jackson are commonly referred to as ''hat acts.'' But Travis Tritt and Marty Stuart, who've both enjoyed top 10 country hits recently (''Anymore'' and ''Tempted,'' respectively), are going against the felt. From now until early next year, the two will be hitting the road as the No Hats Tour. Tritt says, ''I don't think you should wear a hat unless you can ride a horse.'' Besides, he adds, ''Even if we wanted to, we couldn't find cowboy hats to fit over all this hair.''