Joshua says this rematch with Usyk is a big opportunity for him to claim status as a boxing legend. Anthony Joshua isn’t pretending that changes weren’t needed in his camp if he’s to once again rebound to reclaim three major world titles in his Aug. 20 rematch with Oleksandr Usyk. This is sort of familiar territory for Joshua, who dropped all of the titles to Andy Ruiz in one of the biggest surprise upsets of the past few years. Ruiz, however, is not Oleksandr Usyk, so on top of hiring Robert Garcia to be his new lead trainer, Joshua tells…