Marking the continued demise of new weekend series, ABC has crossed out the Saturday hours “Covington Cross” and “Crossroads” and will replace them with repeat “Columbo” telefilms from 8-10 p.m. through the end of the calendar year.By doing so, the network takes the same approach that it used last year on Thursday night and that NBC employed this season by scheduling “Perry Mason” repeats from 8-10 p.m. Fridays. In fact, each of the three networks has been forced to knock out a night of weekend programs and replace new shows with movies, with CBS currently airing repeat theatricals on Saturday following “Brooklyn Bridge.” ABC will burn off episodes of “Covington Cross” and “Crossroads” at a later date but won’t order additional segments. The first, a medieval action hour from Reeves Entertainment, was averaging a 6.6 rating, 12 share in the lead-off hour Saturday, while “Crossroads”–a Robert Urich vehicle from Lorimar TV–had posted a 6.1/10. With the changes, eight of 33 new series introduced this fall are now casualties–three each on NBC and ABC and two on CBS. A fourth NBC series, “Rhythm & Blues,” is on hiatus waiting to return along with ABC’s “The Young Indiana Jones Chronicles” and CBS’ “Raven.” ABC’s “The Commish,” a sophomore series that airs at 10 p.m. Saturdays, should benefit from the change. The show has proven a self-starter throughout the season, averaging a 10.0/19 and rivaling NBC’s “Sisters” in its hour despite poor lead-ins.