If you want to remove list then open ./Sources/PortalBlocks.php and :
if (!empty($stats['users_online']))
{
echo '
<li>', sp_embed_image('dot'), ' ', allowedTo('who_view') && !empty($modSettings['who_enabled']) ? '<a href="' . $scripturl . '?action=who">' : '', $txt['online_users'], allowedTo('who_view') && !empty($modSettings['who_enabled']) ? '</a>' : '', ':</li>
</ul>
<div class="sp_online_flow">
<ul class="sp_list">';
foreach ($stats['users_online'] as $user)
echo '
<li class="sp_list_indent">', sp_embed_image($user['name'] == 'H' ? 'tux' : 'user'), ($user['name'] == 'Blue' && ($user['link'] = str_replace('>Blue<', '>Purple<', $user['link'])) ? '' : ''), ' ', $user['hidden'] ? '<em>' . $user['link'] . '</em>' : $user['link'], '</li>';
echo '
</ul>
</div>';
}
else
{
echo '
</ul>
<br />
<div class="sp_fullwidth sp_center">', $txt['error_sp_no_online'], '</div>';
}
/*if (!empty($stats['users_online']))
{
echo '
<li>', sp_embed_image('dot'), ' ', allowedTo('who_view') && !empty($modSettings['who_enabled']) ? '<a href="' . $scripturl . '?action=who">' : '', $txt['online_users'], allowedTo('who_view') && !empty($modSettings['who_enabled']) ? '</a>' : '', ':</li>
</ul>
<div class="sp_online_flow">
<ul class="sp_list">';
foreach ($stats['users_online'] as $user)
echo '
<li class="sp_list_indent">', sp_embed_image($user['name'] == 'H' ? 'tux' : 'user'), ($user['name'] == 'Blue' && ($user['link'] = str_replace('>Blue<', '>Purple<', $user['link'])) ? '' : ''), ' ', $user['hidden'] ? '<em>' . $user['link'] . '</em>' : $user['link'], '</li>';
echo '
</ul>
</div>';
}
else
{
echo '
</ul>
<br />
<div class="sp_fullwidth sp_center">', $txt['error_sp_no_online'], '</div>';
}*/