DETROIT — A rogue FBI informant tried to keep the Gov. Gretchen Whitmer kidnapping plot alive, obstruct justice and destroy evidence after federal agents arrested more than a dozen men in fall 2020, prosecutors said Friday. The informant, Wisconsin resident Stephen Robeson, urged others to destroy evidence, warned accused plot ringleader Barry Croft that he was wanted by the FBI and told another to destroy evidence by throwing a gun in a lake, according to a court filing. Prosecutors leveled the allegations while trying to prevent Robeson from being called as a defense witness during the ongoi…