Starting today, Air France is giving up its short-lived experiment with "smoker's bars"--curtained-off and specially ventilated areas in cabins--in the U.S. and will ban smoking on all flights involving U.S. destinations. However, the airline will retain smoker's bars on flights from Paris to South America and Asia. . . . Amtrak has replaced Custom Class reserved seating with Pacific Class on its San Diegan trains, between San Diego and San Luis Obispo. Changes include at-seat service by an attendant and, on most routes, renovated, one-level cars with roomier seats, cellular phones and outlets for laptop computers. Upgrades to Pacific Class vary from $9 to $17.