clutter/stage: Remove hide/show cursor API

This removes it from the stage window API too. It's managed by the
mutter backends, so we don't need the stage window to do it as well.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1175

src/tests/clutter/interactive/test-devices.c

@@ -227,7 +227,6 @@ test_devices_main (int argc, char **argv)
   stage = clutter_stage_new ();
   clutter_actor_set_background_color (stage, CLUTTER_COLOR_LightSkyBlue);
   clutter_stage_set_title (CLUTTER_STAGE (stage), "Devices");
-  clutter_stage_hide_cursor (CLUTTER_STAGE (stage));
   g_signal_connect (stage,
                     "destroy", G_CALLBACK (clutter_main_quit),
                     NULL);