By Chris Mannix Kevin Durant isn’t doing his part against Boston. But his coach isn’t putting him in a position to succeed. View the original article to see embedded media. NEW YORK – So now we know why the Celtics didn’t go out of the way to avoid the Nets in the first round, didn’t kick away the season finale (hi, Milwaukee), didn’t sweat the results of the play-in like a high schooler does the SAT. Brooklyn had star power, but no system. An explosive offense that, as it turns out, didn’t have a prayer against the NBA’s stingiest defense. Boston took Game 3 of its first-round series against …