Three Columbia University deans, who engaged in what the school’s administration called troubling “text message exchanges” that touched on “ancient antisemitic tropes,” have resigned, a university spokesperson said late on Thursday. Cristen Kromm, former dean of undergraduate student life; Matthew Patashnick, former associate dean for student and family support; and Susan Chang-Kim, former vice dean and chief administrative officer, were earlier placed on leave as an investigation proceeded. The message exchanges took place during an event on campus titled “Jewish Life on Campus: Past, Present…