Implemented menu deletion on window destruction on the GTK+ backend.
Implemented menu deletion on window destruction on the GTK+ backend.

tbodt/libui,tbodt/libui,ProtonMail/libui,ProtonMail/libui,mantyr/libui,mantyr/libui,sclukey/libui,ProtonMail/libui,sclukey/libui,mantyr/libui