The turmoil at ABC News has taken another twist in the wake of George Stephanopoulos’ remarkable comment declaring President Joe Biden must go — with “private celebrations” from one his fiercest on-air rivals. David Muir, the anchor of ABC World News Tonight and co-anchor of the ABC News magazine 20/20, had been vying for the first broadcast interview with the president in the wake of his disastrous debate performance against Donald Trump that sparked senior Democrats to turn on him and demand his removal from the 2024 ticket. When Biden and his top advisors chose Stephanopoulos, the gulf betw…