For a while it seemed that the box office snoozefest known as January would pack a competitive punch this year with the Jan. 9 release of two remarkably similar-sounding films about presidential offspring: ''Chasing Liberty,'' starring Mandy Moore, and ''First Daughter,'' with Katie Holmes. The race was over, however, before it could begin when ''Daughter'' quietly bowed out. (Twentieth Century Fox will give no reason for the flinch, nor offer a definite date for the film's release.) Curious, given the brash statements of ''Daughter'' producer John Davis. In September, he insisted that his ''bigger and better movie'' would not need to move its release date since Moore's ''rinky-dink version... poses absolutely no competition at the box office.'' Maybe he was right: ''Liberty'' opened to a disappointing $6.1 million.