You're welcome Joan
Unfortunately that was not possible to disable this from backend, but you can modify on this file ->
JoomlaFolder\components\com_easyblog\themes\wireframe\comments\form.php
// Remove line 27 until 32
<?php if ($this->my->guest) { ?>
<div class="pull-right">
<?php echo JText::_('COM_EASYBLOG_COMMENTS_ALREADY_REGISTERED');?>
<a href="<?php echo $loginURL;?>"><?php echo JText::_('COM_EASYBLOG_COMMENTS_ALREADY_REGISTERED_LOGIN_HERE');?></a>
</div>
<?php } ?>