He’s been dead for eight years, but try telling that to the NYPD. Cops have barged into James Jordan Sr.’s family home looking for him more than a dozen times since he died in 2006 — prompting his exasperated relatives to finally post his death certificate on the front door. “I tell them over and over, ‘James isn’t here! He’s dead! It’s that simple. What’s so difficult to understand about that?’ ” the Brooklyn security guard’s widow, Karen, told The Post on Monday. James Jordan Sr., who died from diabetes at age 46, was last arrested in 1996 — for turnstile-jumping,...