gs-shell: Remove app menu
https://wiki.gnome.org/Initiatives/GnomeGoals/AppMenuRetirement
This required the new auth menu to be refactored to support the menu items that used to be in the app menu.
https://wiki.gnome.org/Initiatives/GnomeGoals/AppMenuRetirement
This required the new auth menu to be refactored to support the menu items that used to be in the app menu.