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/x11/window.rs

@@ -1395,21 +1395,11 @@ impl UnownedWindow {
         self.xconn.display as _
     }
 
-    #[inline]
-    pub fn xlib_screen_id(&self) -> c_int {
-        self.screen_id
-    }
-
     #[inline]
     pub fn xlib_window(&self) -> c_ulong {
         self.xwindow as ffi::Window
     }
 
-    #[inline]
-    pub fn xcb_connection(&self) -> *mut c_void {
-        self.xconn.xcb_connection().get_raw_xcb_connection()
-    }
-
     #[inline]
     pub fn set_cursor_icon(&self, cursor: CursorIcon) {
         let old_cursor = replace(&mut *self.cursor.lock().unwrap(), cursor);