The “FBI” season finale, about a student with a stock of weapons, was yanked from the schedule Tuesday, hours after a teenage gunman killed 19 students and two teachers at a Texas elementary school. The episode, titled “Prodigal Son” and meant to air on CBS Tuesday night, was instead replaced by an episode from earlier in the season. “As the team investigates a deadly robbery that garnered a cache of automatic weapons for the killers, they discover one of the perps is a classmate of Jubal’s son, who is reluctant to cooperate,” the logline for the finale reads. Jubal Valentine, played by Jeremy…