btrfs: remove alloc_list splice in btrfs_prepare_sprout

btrfs_prepare_sprout is called when the first rw device is added to a
seed filesystem. This means the filesystem can't have its alloc_list
be non-empty, since seed filesystems are read only. Simply remove the
code altogether.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -2391,10 +2391,6 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
 	list_for_each_entry(device, &seed_devices->devices, dev_list)
 		device->fs_devices = seed_devices;
 
-	mutex_lock(&fs_info->chunk_mutex);
-	list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list);
-	mutex_unlock(&fs_info->chunk_mutex);
-
 	fs_devices->seeding = false;
 	fs_devices->num_devices = 0;
 	fs_devices->open_devices = 0;