Chicago’s top federal prosecutor appears to be shifting the focus of criminal cases brought against defendants arrested in sting operations involving fake “stash houses.” In motions filed this month in seven separate cases, U.S. Attorney Zachary T. Fardon’s office asked that drug-conspiracy charges against a total of 27 defendants be dismissed. Some of the motions have been granted. Others are pending, but judges typically grant such requests from prosecutors. The defendants are still …