By Denny Dyroff, Entertainment Editor, The Times Summer Horns A few months ago, Dave Koz & Friends returned to the concert trail with the “Summer Horns 2021 Tour.” The tour will visit the Delaware Valley this weekend with a show on September 17 at Rivers Casino (1001 North Delaware Avenue, Philadelphia, www.riverscasino.com). On the “Summer Horns 2021 Tour,” Koz has been joined by a trio...