Reuters: BP Plc’s ruptured Gulf of Mexico well that caused the biggest U.S. offshore oil spill ever could be killed for good within four days, the U.S. official overseeing the spill response said on Wednesday. “Four days from now it can all be done,” retired Coast Guard Admiral Thad Allen told reporters at a briefing in Kenner, Louisiana. That will end the seabed chapter of the disaster that started with a blowout on April 20 that led to an explosion aboard the Deepwater Horizon …