The Casino Royale, the last theater in downtown Washington showing X-rated pornographic movies, has become the victim of urban development. Workmen moved in over the weekend to prepare to demolish the theater that is located two blocks from the White House. The marquee still listed the last double feature, "Bring on the Virgins" and "Passionfest." The theater and an adjoining adult bookstore are giving way to an office building. The Casino Royale was in the heart of the block which until recently also had a massage parlor and clubs featuring nude dancers and X-rated videos. Two other theaters in the Washington area still show full length adult films. One is in a northeast neighborhood and the other is in a shopping mall in the city's Virginia suburbs.