NEW YORK—An 87-year-old singing coach street died Tuesday of head injuries from being shoved to the ground on a New York City street, police said while searching for a suspect in what a top official called “an unprovoked, senseless attack.” Barbara Maier Gustern, who had worked with performers on Broadway and beyond, hit her head and was critically injured in the attack Thursday night. A woman crossed the street, came up behind Gustern and pushed her to the ground on West 23rd Street in Manhattan’s Chelsea neighborhood, according to police, who have released surveillance video of the suspect. Chief of Detectives James Essig said the assault was “an unprovoked, senseless attack.” “That’s horrific. An 87-year-old woman, just walking down the street, knocked to the ground,” Essig said at a news conference Tuesday, deploring the “disgusting and disgraceful offense.” Friends told The New York Times that Gustern had just left her …