SEASON PREMIERE: Each fall, on broadcast TV, is a mixture of new shows hoping to elbow their way into the prime-time lineup and returning shows determined to prove they still have life and legs.  Today’s TV schedule features two very old dogs who have survived not only for years, but for decades. For the CBS newsmagazine 48 Hours, which premiered in 1988, tonight’s program marks its Season 32 premiere, making it one of the oldest current shows on broadcast TV. The granddaddy remains another CBS newsmagazine, 60 Minutes, which premiered in 1968. On tonight’s 48 Hours: “Click for a Killer,” a report about hit men found and hired on the deep web.