ATLANTA — The Atlanta Hawks on Friday entered a painfully early start to their offseason of uncertainty. After advancing to the second round of the playoffs three straight years, the Hawks were eliminated in the first round with Thursday night’s Game 6 loss at Boston. Atlanta’s players, bleary from lack of sleep, were told by coach Larry Drew in a final team meeting on Friday morning they should be proud of winning 40 regular-season games despite losing All-Star center Al Horford for almost the full season.