Massive snow piles were still clogging up streets near Big Apple hospitals more than a week after deadly Winter Storm Fern — creating dangerous obstacles for emergency responders, The Post has learned. Several EMS workers at New York-Presbyterian Weill Cornell Medical Center on Monday said they’re having serious trouble maneuvering between the snowy mountains, with a Post reporter observing at least six blaring ambulances stuck in gridlock traffic along York Avenue. “This is one of the worst