His departure from public life was nasty, dramatic and well-documented. But former Orange County Sheriff Mike Carona got out of prison this week in a far different manner: Quietly, and somewhat mysteriously. Carona, 59, has left a federal prison medical center in Lexington, Ky., said Kenny Coleman, the center’s camp administrator, on Thursday. Carona served 52 months of a 66-month sentence for felony witness tampering.