By Stephanie Apstein Even if Kamila Valieva had never tested positive for a banned substance, the 15-year-old shouldn’t have been able to qualify for the Olympics. BEIJING — Kamila Valieva should not be skating at the Olympics. Not just because she failed a drug test taken Christmas Day. Not just because she competes for the Russian Olympic Committee, a shell corporation for Russia. Not just because this whole event has become a sham. Valieva should not be skating at the Olympics because she is 15 years old. Children should compete against children. Adults should compete against adults. The va…