Two separate Suffolk County murder convictions have been upheld by the Supreme Judicial Court, District Attorney Daniel F. Conley’s office said. On Oct. 15, the high court affirmed the first-degree murder conviction of Joseph P. Lennon, 54, for the 2006 stabbing of a 42-year-old homeless man near Faneuil Hall, Conley’s office said. In an unrelated case Monday, the court also affirmed the first-degree murder conviction of Darryl Scott, 31, for shooting and killing a teenager outside a downtown Boston movie theater in 2003, the statement said.