Sydney Opera House, November 5 After a year dominated by Giselle, Frederick Ashton’s The Dream, Alexei Ratmansky’s Cinderella, the lavish new Sleeping Beauty and Graeme Murphy’s Swan Lake, the dancers of The Australian Ballet were undoubtedly delighted to dive into the pared-back costumes and sharp-edged choreography of 20:21 (the title refers to the 20th and…