drivers: lustre: obdclass: simplify unregister_shrinker() usage

lu_global_fini() explicitly uses knowledge about shrinker's
internals to make decision about calling of unregister_shrinker().
Now this check was integrated into unregister_shrinker(),
so it is safe to call it against unregistered shrinker.
Signed-off-by: Aliaksei Karaliou <akaraliou.dev@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/obdclass/lu_object.c

@@ -1977,7 +1977,6 @@ int lu_global_init(void)
  */
 void lu_global_fini(void)
 {
-	if (lu_site_shrinker.nr_deferred)
 	unregister_shrinker(&lu_site_shrinker);
 	lu_context_key_degister(&lu_global_key);