Pennsylvania prosecutors are dropping their grand jury subpoena to Twitter demanding the identity of two account holders who have used the micro-blogging service to disparage Attorney General Tom Corbett, a spokesman said Friday. Corbett, the Republican candidate for governor, was seeking to unmask the account holders ahead of Friday’s sentencing of Brett Cott, whom Corbett ensnared  in a political corruption investigation. Corbett wanted to know if Cott was the one anonymously disparaging Corbett and the ongoing probe known as “Bonusgate,” Corbett spokesman Kevin Harley said in a telephone interview. Prosecutors believed that linking Cott to one of the Twitter accounts ...