By Kanishka Singh WASHINGTON (Reuters) – Airlines canceled nearly 2,000 U.S. flights as of Saturday morning following a massive winter storm that snarled airport operations around the United States and frustrated thousands of holiday travelers. Total flight delays within, into or out of the United States amounted to about 4,000 as of Saturday morning, according to flight tracking website FlightAware, which showed that total U.S. flight cancellations stood at around 2,000. The flight cancellations on Saturday morning included over 450 from Southwest Airlines and nearly 400 from Delta Air Lines …