CHICAGO, Oct 30 (Reuters) - Delta Air Lines and AMR Corp's American Airlines raised fares by $6 to $10 on domestic round trips on Friday, completing the sixth industrywide increase of 2009, a top airfare expert said. The moves reflect new pricing power by U.S. airlines as they claw their way out of an economic downturn that eroded travel demand and forced them to slash capacity. Major U.S ...