output: remove XRGB8888 cursor fallback format

All graphics drivers supporting cursor planes support ARGB8888,
the default cursor format, so this fallback is almost certainly
unused.

Essentially all cursor themes use alpha transparency to make it
clearer where relative to the screen content the cursor hotspot is.
It is better to fall back to a slightly slower software cursor than
it is to fall back to the opaque square that is a hardware cursor
without an alpha channel.

types/output/cursor.c

@@ -206,13 +206,7 @@ static struct wlr_drm_format *output_pick_cursor_format(struct wlr_output *outpu
 		}
 	}
 
-	struct wlr_drm_format *format = output_pick_format(output, display_formats,
-		DRM_FORMAT_ARGB8888);
-	if (format == NULL) {
-		format = output_pick_format(output, display_formats,
-			DRM_FORMAT_XRGB8888);
-	}
-	return format;
+	return output_pick_format(output, display_formats, DRM_FORMAT_ARGB8888);
 }
 
 static struct wlr_buffer *render_cursor_buffer(struct wlr_output_cursor *cursor) {