“Musical theater was once a staple of television. Throughout the 1950s and ’60s, ‘The Ed Sullivan Show’ regularly featured performances from the latest Broadway shows, allowing people who had little prospect of seeing the productions to get at least a taste of them. In the mid-’50s, when Mary Martin brought “Peter Pan” to NBC, it was a national event — one that the network repeated regularly for years. Televised productions of such musicals as “Wonderful Town,” “Annie Get Your Gun,” “One Touch of Venus,” “Brigadoon” and “Kiss Me, Kate,” among others, also were presented during that era. Where did it all go?”