udev: rename udev_rules_unref() to udev_rules_free()

As udev_rules do not have a reference counter.

src/test/test-udev.c

@@ -55,7 +55,7 @@ static int fake_filesystems(void) {
 }
 
 static int run(int argc, char *argv[]) {
-        _cleanup_(udev_rules_unrefp) struct udev_rules *rules = NULL;
+        _cleanup_(udev_rules_freep) struct udev_rules *rules = NULL;
         _cleanup_(udev_event_freep) struct udev_event *event = NULL;
         _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
         const char *devpath, *devname, *action;