Six-plus months after the fact, the Rangers’ second-round, six-game playoff defeat to Ottawa that ultimately broke up that old gang on Broadway remains difficult to fathom. If it wasn’t quite the 1960 World Series, in which the Yankees outscored the Pirates 55-27 yet lost in seven games, the series was one-sided enough through the first five games in which the Blueshirts led for 179:52 and trailed for all of 13:10 but still were down 3-2 in the series they’d lose with a miserable effort in a Game 6 defeat at the Garden. The playoff ouster that followed a rousing six-game opening round victory over Montreal presaged the departures of Bluebloods Dan Girardi and Derek Stepan and represents one of the more deflating exits from the postseason over the last 50 years. Not that the Rangers were necessarily thinking about that when the Senators came to the Garden on Sunday. There were other things on the minds of the Blueshirts, who had lost two straight and had won only nine of their first 20 games (9-9-2) entering the contest. Except, that is, on the mind of Henrik Lundqvist. “Benny reminded me about it at the morning skate,” Lundqvist told The Post, alluding to the goalie whisperer, Benoit Allaire. “It kind of stunk a little bit, too, him telling me that these are the guys that knocked me and us out.