By David Shepardson WASHINGTON (Reuters) -A federal judge in Florida said on Monday a U.S. mask mandate on public transportation is unlawful, overturning a Biden administration effort to reduce the spread of COVID-19. Last week, U.S. health officials extended by 15 days the mandate requiring travelers to wear masks on airplanes, trains, and in taxis, ride-share vehicles or transit hubs, saying they needed time to assess the impact of a recent rise in COVID-19 cases. The ruling by U.S. District Judge Kathryn Kimball Mizelle, an appointee of President Donald Trump, came in a lawsuit filed last y…