In a revealing retrospective, the beloved cast of “Seinfeld” has resurfaced in a way that might leave fans gasping—time has not been kind to the stars of the legendary sitcom. Originally airing from 1989 to 1998, “Seinfeld” redefined television comedy with its sharp wit and unforgettable characters, but two decades later, the changes in the actors who brought Jerry, George, Elaine, and Kramer to life are startling.