The Celtics are excited to have Jrue Holiday. That was clear two days ago when Brad Stevens couldn’t stop gushing about his newly acquired guard, declaring him one of the only guys in the league worth giving up Robert Williams in a deal. That was clear when Stevens, seated to Holiday’s left at the Auerbach Center, grinned like he just got away with highway robbery for most of the nearly half hour introductory press conference. And it was clear from how eager Joe Mazzulla was to get Holiday up to speed.