btrfs: do not check delayed items are empty for single transaction cleanup

btrfs_assert_delayed_root_empty() will check if the delayed root is
completely empty, but this is a filesystem-wide check.  On cleanup we
may have allowed other transactions to begin, for whatever reason, and
thus the delayed root is not empty.

So remove this check from cleanup_one_transation().  This however can
stay in btrfs_cleanup_transaction(), because it checks only after all of
the transactions have been properly cleaned up, and thus is valid.

CC: stable@vger.kernel.org # 4.4+
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NNikolay Borisov <nborisov@suse.com>
Reviewed-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -4503,7 +4503,6 @@ void btrfs_cleanup_one_transaction(struct btrfs_transaction *cur_trans,
 	wake_up(&fs_info->transaction_wait);
 
 	btrfs_destroy_delayed_inodes(fs_info);
-	btrfs_assert_delayed_root_empty(fs_info);
 
 	btrfs_destroy_marked_extents(fs_info, &cur_trans->dirty_pages,
 				     EXTENT_DIRTY);