They’re still hopelessly devoted to Olivia Newton-John. Newton-John, who died Monday at age 73, is being remember by the London production of “Grease the Musical,” which dedicated its upcoming performances to the star, according to Entertainment Weekly. “She is an icon who has inspired countless young performers across the world, especially all of us in this company,” Olivia Moore, who plays the Sandy character made famous by Newton-John in the 1978 “Grease” movie, said after Tuesday’s show on the West End. “It is a huge honor to follow in Olivia’s footsteps each night and perform those songs …