Vengeful O.J. Simpson was reportedly on a rampage to kill a tell-all book by his former prison cellmate and confidant before he died, RadarOnline.com has learned. Simpson, 76, died on Wednesday after a battle with cancer. Now, sources claim he worked overtime in his final years to keep his secrets concealed. Reps for the disgraced NFL star allegedly offered $5,000 to Vernon Johnson — who shared a cell with “The Juice” between 2015 and 2016 — in a desperate bid to buy his silence. According to the National Enquirer, sources said Vernon, who is serving a 20-year sentence for assault and battery,…