With roughly a trillion shows on TV, the ending of a series is no longer the “cancel all my plans” event it once was. Nowadays it’s hard to imagine that the 1983 finale of “M*A*S*H” was watched by a staggering 106 million people — nearly half the country at the time. Or that “Cheers’” last episode snagged 84 million viewers in 1993. And that, in 1998, 76 million tuned in for the controversial closer of “Seinfeld.” Sunday night’s finale of HBO’s “Curb Your Enthusiasm,” by “Seinfeld” creator Larry David, won’t do numbers like those. Not even pretty … pretty …...