Only in Philadelphia could a politician who went up the river for racketeering, mail fraud, tax evasion and obstruction of justice come home to a hero’s welcome. Former City Councilman Jimmy Tayoun, one of the city’s most colorful political felons, came home yesterday after almost three years in jail. He flashed a million-dollar smile as he got off a Capitol Trailways bus in the dark and dirty 11th Street tunnel outside the Peter Pan bus terminal.