A federal judge has agreed to decrease by 810,000 barrels the amount of oil claimed to have spilled into the Gulf of Mexico during the 2010 Deepwater Horizon disaster, which would reduce the potential maximum penalty for Clean Water Act violations by $3.4 billion. BP Plc (NYSE: BP) had made the argument to U.S. District Judge Carl Barbier in New Orleans that those particular barrels weren’t released into the environment. Bloomberg is reporting that Barbier concluded the 810,000 barrels shouldn’t…