SERIES FINALE: Sabado Gigante, the longest-running variety series in TV history, calls it quits tonight after 53 years on the air, with a live episode simulcast in the U.S., Chile and Mexico. Mario Luis Kreutzenberger Blumenfeld, the Chilean host known as Don Francisco, presides over the three-hour extravaganza one last time, making room not only for the standard supporting characters and models, but also for such grateful guest stars as Shakira, Marc Anthony, Gloria Estefan, and Enrique Iglesia