BOSTON — If Ben Simmons is going to play a playoff game this season, the decision will be his, not anyone else’s. That’s the message Nets head coach Steve Nash delivered hours ahead of tipoff for Game 2 against the Celtics on Wednesday, 10 months after Simmons last played in an NBA game. “There’s no other way than him to say, ‘I’m ready,’ especially after an absence this long,” Nash said at TD Garden. “So whenever he is ready, it’s gonna have to be on him to say, ‘I feel comfortable,’ ‘I feel ready to go,’ ‘I want to play,’ ‘I want to contribute.’ We can’t push him places when you have been ou…