I don't think that it's "Dirty Old Town", which never mentions Salford by name.  The Dubliners appear to have recorded a "Salford Town" (as well), described as traditional (though as we know, that's far from a guarantee that it is), and that's all I could discover.  The only site I found that claimed to have the lyrics was a mass of broken links.  One for the Dubliners fans, perhaps...

Malcolm