Barnes & Noble has announced plans to close its three-story location in downtown Bethesda, an institution for more than two decades at the corner of Woodmont and Bethesda Avenues. The departure, scheduled for the end of this year, will leave the struggling bookseller with just two stores in Montgomery County: one at Montrose Crossing on Rockville Pike, and the other at Rio Washingtonian Center in Gaithersburg.