With Thursday’s debut of “House Hunters: Comedians on Couches,” HGTV is officially in the business of making fun of itself. In the quarantine-TV show, hosts Dan Levy (not the “Schitt’s Creek” one, the other one), Natasha Leggero, and a revolving door of their stand-up comedian friends watch-party a classic episode of “House Hunters” and then take turns taking the home buyers down a peg or two.