Do a forum search for "preemption" and you should find the discussion you're looking for.
Basically, municipalities can only prohibit firearms on municipal property, such as fair grounds. Basically only places they have a right to permanently fence off and keep people out of. This would not include public streets & sidewalks.
Many localities still have such laws on the books. They're basically just there because the bureaucrats are too lazy to remove them. Maybe they even want people to think they're still in force. Who knows.
Usual disclaimer: I'm not an attorney and this is not legal advice.