BOSTON — Whether it was gamesmanship or pure candor from Dallas’ head coach, Jason Kidd’s proclamation of Jaylen Brown being Boston’s best player certainly shifted a blistering spotlight back onto the battle that’s brewed throughout Brown and Jayson Tatum’s seven seasons together. It’s been a fight for these Celtics to resist the temptations of external antagonism, to the point Jrue Holiday felt the need to clarify his statement on the matter from Saturday’s practice, before Holiday took questions from the media following his team-high 26 points in the Celtics’ 105-98 Game 2 win over the Mavericks Sunday night.