BOSTON — Massachusetts prosecutors said Thursday that they will dismiss more than 6,000 convictions tied to a former chemist who authorities say was high almost every day she worked at a state drug lab for eight years.The move comes months after the American Civil Liberties Union and the state’s public defender agency asked the state’s highest court to throw out all of the cases tainted by Sonja Farak, who pleaded guilty in 2014 to stealing drugs from the state crime lab at the University of Massachusetts …