After a must win in Milwaukee, the Celtics head home to cap off an amazing second round. “The best two words in basketball are ‘Game 7,’” Jaylen Brown said after the Celtics beat the Bucks 108-95 in Milwaukee in a must-win Game 6. After squandering homecourt advantage two nights prior back in Boston, they’ll now head back to TD Garden for a Sunday afternoon series-ending showdown with the defending champs. Recall a month ago when the Celtics, Bucks, and 76ers all had the opportunity to secure the second seed in the Eastern Conference on the final day of the regular…