Remove `--label` option from `test/scripts/daos_pool.sh.in`.

[hyoklee]

It will not work for DAOS 2.3.

See also #48

[jhendersonHDF]

See daos-stack/daos@9619d36. The --label option seems to have been removed in favor of specifying the pool label as a positional argument. We should revisit what DAOS version we want to support with the latest development branch of the DAOS VOL.