Why don't you remove directly in Interface Builder ?
Have you defined an IBOutlet for the menuBar ?
@IBOutlet weak fileprivate var menuBar: NSMenu!
Edit your storyboard or xib. Removing them via code as Claude31 suggested is correct if you're bound and determined not to edit the resources.
Actually, If you go the programmatic way, it is recommended to do that in applicationWillFinishLaunching, before the system inserts some of it's own menu items. I'm sorry I can't find the link to where I've read that (I think it was a technical note or a release note), but I remember it was from Apple.
Hope it helps.