CHICAGO — Cook County prosecutors on Wednesday dropped charges against two Chicago police officers who were accused of beating a teenager after a car chase. Officers Jeffery Shafer, 38, and Victor Guebara, 42, were charged with six felony counts of aggravated battery and official misconduct after prosecutors said they punched a teenage boy in the face and head while he was on the ground about to be arrested. Prosecutors dropped the charges in front of a courtroom packed with police officers after the alleged victim in this case failed to appear in court as a bench trial before Judge Angela Pet…