Duke University has removed from students what has become one of the most significant aspects of matriculation at many colleges: picking a first-year roommate.  Beginning with the Class of 2022, the roommate-selection process will be entirely governed by the university, with assignments largely made at random -- a shift, officials said, meant to stem the recent movement of students self-selecting peers with similar perspectives and backgrounds to their own, fueled by social media connections made before arriving on campus.