notifier: switch to QLIST

Notifiers do not need to access both ends of the list, and using
a QLIST also simplifies the API.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/vl.c b/vl.c
index 9609d2b..d8a521a 100644
--- a/vl.c
+++ b/vl.c
@@ -2093,7 +2093,7 @@
 
 void qemu_remove_exit_notifier(Notifier *notify)
 {
-    notifier_list_remove(&exit_notifiers, notify);
+    notifier_remove(notify);
 }
 
 static void qemu_run_exit_notifiers(void)