As per summary. The Folder / Mailing List Management menu item seems to be unnecessary as it's identical to Folder / Folder Properties.
Hello, not a dev, just a triager here. I'm not really sure if removing this is necessary. Aside from the option "Mailing list management" in the Folder menu and "Mailing list name" in the Message menu (which requires having already set a mailing list folder), there's no immediate way to demonstrate to a new user that KMail can handle mailing lists, like a context menu entry. Without it, the user would have to open the folder properties and notice the last tab before they get to know this exists.