Remove superfluous fflush call

The blame reveals commit 820cfe73, which introduced printing of
notifications similar to notification_print(). The fflush call is still
left over since porting the printfs into their dedicated method.

As notification_print() is called after this fflush() call, it's not
necessary anymore.

src/dbus.c

@@ -258,8 +258,6 @@ static struct notification *dbus_message_to_notification(const gchar *sender, GV
                 g_variant_iter_free(iter);
         }
 
-        fflush(stdout);
-
         if (n->actions->count < 1)
                 g_clear_pointer(&n->actions, actions_free);