Wayne State University prevented a group of peaceful pro-Palestinian activists, including students and professors, from gathering at a campus site, the latest example of the college cracking down on opponents of Israel’s relentless killings in the Middle East. Organizers were surprised when campus police told them on Friday they were not allowed to hold their vigil and pop-up clinic in front of the Mazurek Medical Education Commons on East Canfield, less than two months after they got permission for their biweekly gatherings.