Jem Aswad Senior Music EditorAfter unveiling it during a performance at Boston’s Fenway Park on Tuesday, Guns N’ Roses have released “Absurd,” their first official new song since their 2008 album “Chinese Democracy.”However, to call the song “new” is a relative term: The song, formerly called “Silkworms,” has been knocking around for two decades and was reportedly written during the years of sessions for “Chinese Democracy.”The fast-paced track features Axl Rose singing with an almost comical