Hopefully, it was the continuing cold weather that kept people away from last week’s concerts by the National Symphony Orchestra, rather than the pathetic provincialism of Washington audiences, wary of too much modern music. If the latter is true, the names of violinist Renaud Capuçon and cellist Gautier Capuçon should have been enough to get listeners through the doors. At the Friday night concert, they played the Brahms violin and cello concerto (A minor, op….