By Pete Schroeder WASHINGTON (Reuters) -A senior attorney with the Federal Deposit Insurance Corporation has pleaded guilty to one charge of sexually exploiting children, the U.S. Justice Department announced late Tuesday. Mark Black, 50, was a member of two online groups dedicated to finding prepubescent girls and convincing them to livestream themselves engaging in sexually explicit content, the Justice Department said. Black had most recently worked as special counsel in the office of the FDIC’s general counsel, according to his LinkedIn profile. He had been with the FDIC since 2013. An FDI…