The Met’s 1979 telecast of Mahagonny exposed one of the lesser-known factors contributing to the demise of disco:  the global supply of eye shadow, rouge and lip gloss was exhausted for the next decade by a cast featuring Klara Barlow, Louise Wohlafka, Nedda Casei, Gwynn Cornell, Joann Grillo and Isola Jones—and stilettos, garter belts and…