From simple location-tracking apps to buttons that measure biometrics, college campuses have amped up surveillance in response to Covid-19 — Vassar College student E.L. received a notification on his phone this month with a gentle reminder to turn on his device’s location tracking. The junior, who asked that only his initials be used, is one of the 2,120 students who returned to Vassar’s campus for in-person instruction this fall semester…