THE next time the FCC complains about How ard Stern, Viacom has promised to yank him off the air immediately. The unusual "sudden death" deal is part of a sweeping, $3.5 million consent decree announced yesterday by the FCC that wipes out "at least 50" indecency investigations against all of Viacom's radio and TV stations — including several against Stern, as well as Opie & Anthony's $357,000 fine for their infamous "Sex in St. Pat's" contest. It does not include the $550,00 fine against CBS for Janet Jackson's Super Bowl flash, which the network has vowed to fight in...