A racial epithet referring to people of Chinese descent that was used by comedian Sarah Silverman on “Late Night with Conan O’Brien” should have been removed from the broadcast, NBC admitted in the wake of a protest by the watchdog group Media Action Network for Asian Americans. The joke, said the network in a statement released this week, “was clearly inappropriate, and the fact that it was not edited by our standards and practices department was a mistake. We have reviewed our procedures to ensure such an incident does not reoccur and we will edit the joke out of any future repeats of the show.” Guy Aoki, president of the watchdog group, called NBC’s statement “a nice start” — but not enough. “It’s one thing for NBC to apologize on behalf of one of its shows and another for the show to address it,” he said. “I think Conan should say something happened last week that was inappropriate and we apologize if we hurt anybody.” In a similar recent development on “Late Show with David Letterman,” the CBS host offended the country of Colombia with remarks about the drug trade and the Miss Colombia contestant in the Miss Universe contest. The upshot was that she got to appear on the air with Dave, who apologized.