WASHINGTON — A specter is haunting academia, the specter of specters — ghosts, goblins and “cultural appropriation” through insensitive Halloween costumes. Institutions of higher education are engaged in the low comedy of avoiding the agonies of Yale. Last October, the university was rocked to its 315-year-old foundations by the wife of a residential college master (a title subsequently expunged from Yale’s vocabulary lest it trigger traumas by reminding people that slavery once existed).