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

btrfs_assert_delayed_root_empty() will check if the delayed root is
completely empty, but this is a fs 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.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>