By Liza Dobkina ST. PETERSBURG, Russia (Reuters) - U.S. pop singer Selena Gomez has scrapped two concerts in Russia after falling foul of new visa rules which critics say can be used to keep out Western artists who promote gay rights. The concert organizers said the "Come and Get It" singer pulled out of the planned performances in St. Petersburg and Moscow next week when it became clear she would not be able to secure a visa in time. ...