Major news hit the 49ers’ quarterback unit Tuesday, two days after the defending NFC champions were eliminated from playoff contention. — Nick Mullens, who went 2-6 as a fill-in starter this season, is facing Tommy John surgery to repair an elbow injury he sustained in Sunday’s loss at Dallas. — Jimmy Garoppolo is cleared to resume practicing but coach Kyle Shanahan does not plan to play him the remaining two games. — C.J. Beathard will start Saturday against the host Arizona Cardinals, two years after his last start came against them at State Farm Stadium. — Josh Johnson, a veteran safeguard …
