NEW YORK — If he had to do it all over again, Billy Hunter still would have walked out of the negotiating room. That was the defiant tone Hunter struck Thursday as the NBA players’ union held a news briefing at its headquarters in Harlem after owners and players decided they would resume discussions Saturday afternoon for the first time since their acrimonious blowup last Friday. At that meeting, after two days of discernible progress, Hunter and the players’ union representatives walked out of the room