FERGUSON, Mo. — Ferguson’s city attorney has announced plans to step down, just a few weeks after the St. Louis suburb engulfed in racial unrest since Michael Brown’s 2014 death announced they were replacing her as local prosecutor.Stephanie Karr, Ferguson’s city attorney since 2004 and prosecutor since 2011, announced her resignation earlier this week in writing, calling the decision “mine alone” and pledging to stay on the job until her successor is hired.Karr’s departure marks …