Cutrone’s eclectic accomplishments was a 10-year stint as an assistant to Andy Warhol, a number of whose early pictures he helped realize with brush, or in the metallic “Oxidations” paintings, his bodily fluids. When the artist Ronnie Cutrone died late last month, at 65 and apparently of natural causes, a quirky and marginal figure slipped off the cultural stage, taking with him a large and vital hunk of late-20th-century New York history.