You can't hide the menu bar on OS X from within Emacs. It's always shown for non-fullscreen applications, that's simply how OS X works. Applications have no influence on that.
No menu bar
If you'd like to use Emacs without any menu bar, enable fullscreen mode with M-x toggle-frame-fullscreen
.
Removing individual items
If you'd just like to remove individual items from the menu bar, adjust the corresponding key maps in your init.el
. For instance, the following snippet removes the “Options”, “Edit” and ”Tools” menus:
(define-key global-map [menu-bar options] nil)
(define-key global-map [menu-bar edit] nil)
(define-key global-map [menu-bar tools] nil)
A mailing list post from Xah Lee has more examples.