The best coming-of-age stories derive their power from being endings as much as beginnings. There’s often a clarifying, poignant harshness in the losses they depict. That applies — with sobering grace — to the memory ballad “Amrum,” set on Germany’s titular North Sea island in 1945, when the winds of a world war’s conclusion blow into a 12-year-old boy’s life with unexpected consequences.The movie bears a curious credit: “A Hark Bohm film by Fatih Akin.” Bohm, who died last year at 86, was a highly respected film writer, actor and academic, a veteran of Germany’s New Wave. Realizing he’d be...