[metacity] screen: fix cast-function-type warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 49fd2b003c1b6720f4502aeb897192e5f285f11f
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Sep 2 14:16:58 2018 +0300

    screen: fix cast-function-type warning

 src/core/screen.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)
---
diff --git a/src/core/screen.c b/src/core/screen.c
index 7f9e0b81..aec8f11f 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -568,9 +568,7 @@ meta_screen_free (MetaScreen *screen,
   meta_screen_ungrab_keys (screen);
 
 #ifdef HAVE_STARTUP_NOTIFICATION
-  g_slist_foreach (screen->startup_sequences,
-                   (GFunc) sn_startup_sequence_unref, NULL);
-  g_slist_free (screen->startup_sequences);
+  g_slist_free_full (screen->startup_sequences, (GDestroyNotify) sn_startup_sequence_unref);
   screen->startup_sequences = NULL;
 
   if (screen->startup_sequence_timeout != 0)