cursor-renderer-native: Cleanup type declaration

Use G_DECLARE_FINAL_TYPE instead of the old macros.

https://bugzilla.gnome.org/show_bug.cgi?id=785381

src/backends/native/meta-cursor-renderer-native.c

@@ -65,6 +65,11 @@
 
 static GQuark quark_cursor_sprite = 0;
 
+struct _MetaCursorRendererNative
+{
+  MetaCursorRenderer parent;
+};
+
 struct _MetaCursorRendererNativePrivate
 {
   gboolean hw_state_invalidated;