Remove functionality already exposed through raw-window-handle

Nothing changed from the user point of view, other than they should
use the `raw-window-handle`, which is objectively better, given that
it reduces the amount of `cfg` guards in downstream code.

src/platform_impl/linux/wayland/window/mod.rs

@@ -606,11 +606,6 @@ impl Window {
         self.window_state.lock().unwrap().set_ime_purpose(purpose);
     }
 
-    #[inline]
-    pub fn display(&self) -> &WlDisplay {
-        &self.display
-    }
-
     #[inline]
     pub fn surface(&self) -> &WlSurface {
         self.window.wl_surface()