CBS News is already backtracking on a revamp of its “Evening News” program — and the network’s embattled boss risks becoming a casualty, The Post has learned. Just weeks after a drastic overhaul replaced Norah O’Donnell with a “60 Minutes”-style news magazine helmed by a pair of little-known anchors, the Tiffany Network is reverting to a more news-driven broadcast as ratings tumble, sources said. That’s after embarrassments like last week, when the “Evening News” led with “Why can’t Johnny read?” — a six-minute feature package about student literacy — despite a busy news cycle that included Elon Musk appearing at...