You know it’s a recession when leggy Las Vegas showgirls can’t sell enough tickets to stay in business. That’s what’s happening to “Les Folies Bergere,” a revue modeled after its famous namesake in Paris, that has run in Vegas for nearly 50 years. The curtain will go down on the act for the last time on March 28, according to the Tropicana Las Vegas, where the show runs on the Strip