Remove bcopy(), bzero(), bcmp()

bcopy() has a confusing argument order and is actually a move, not a
copy; they're all deprecated since POSIX.1-2001 and removed in -2008,
and we shim them out to mem*() on Linux anyway

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12996

module/zfs/dataset_kstats.c

@@ -123,7 +123,7 @@ dataset_kstats_create(dataset_kstats_t *dk, objset_t *objset)
 
 	dataset_kstat_values_t *dk_kstats =
 	    kmem_alloc(sizeof (empty_dataset_kstats), KM_SLEEP);
-	bcopy(&empty_dataset_kstats, dk_kstats,
+	memcpy(dk_kstats, &empty_dataset_kstats,
 	    sizeof (empty_dataset_kstats));
 
 	char *ds_name = kmem_zalloc(ZFS_MAX_DATASET_NAME_LEN, KM_SLEEP);