al_destroy_menu - Man Page
Allegro 5 API
#include <allegro5/allegro_native_dialog.h> void al_destroy_menu(ALLEGRO_MENU *menu)
Destroys an entire menu, including its sub-menus. Any references to it or a sub-menu are no longer valid. It is safe to call this on a menu that is currently being displayed.
Allegro reference manual