CHICAGO (AP) — The U.S. attorney's office in Chicago has quietly dropped dozens of serious narcotics conspiracy charges stemming from undercover stings involving fictional drug stash houses, a federal law enforcement technique critics contend amounts to entrapment and displays racial bias against minorities. U.S. Attorney Zachary Fardon's office this month moved to dismiss the charges — which carry mandatory minimum prison terms of 10 or 20 years — for 27 out of a total of 33 suspects whose cases are still pending in the district. The spokesman for the U.S.