qemu-iotests: remove comment about root privileges requirement

The check script contains a commented out root user requirement,
probably because of its xfstests heritage.  This requirement doesn't
apply to qemu-iotests, so it better be gone.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
