Using the following steps you can disable the global menu. There are some issues with this approach so read the issues list before continuing. This guide is based on this web upd8 article and this blog post.

Issues

• Maximized applications still have the window controls (i.e. the close, minimize, and resize buttons) on the global menu and you need to hover over the global menu to access them. Non-maximized applications do not have this issue.
• Some applications will still continue to use the global menu after this modification. These need to be fixed manually. In Firefox, for example, a plugin needs to be disabled.

Disable the global menu

• Disable global menu integration in gnome apps (Most importantly, nautilus)

    gsettings set org.gnome.settings-daemon.plugins.xsettings overrides '@a{sv} {"Gtk/ShellShowsAppMenu": <int32 0>}'
  

• Create /etc/X11/Xsession.d/81ubuntumenuproxy

    sudo gedit /etc/X11/Xsession.d/81ubuntumenuproxy
    ...
    export UBUNTU_MENUPROXY=0
  

• Restart your computer

• If any applications still use the global menu they probably use some alternative integration mechanism and need to be dealt with individually. In Firefox the Global Menu Bar Integration plugin needs to be disabled.

Re-enable the global menu

• Delete /etc/X11/Xsession.d/81ubuntumenuproxy

    sudo rm /etc/X11/Xsession.d/81ubuntumenuproxy
  

• Re-enable global menu integration in gnome apps

    gsettings set org.gnome.settings-daemon.plugins.xsettings overrides '@a{sv} {}'
  

• Restart your computer

• Re-enable the global menu integration plugins for any applications that use an alternative integration mechanism.