If you want to remove title - just disable this field in JComments settings (see second tab with view and layout settings). If you want to remove all this string from template - edit file /components/com_jcomments/tpl/default/tpl_comment.php and remove:
<?php
if (($this->getVar('comment-show-title') > 0) && ($comment->title != '')) {
?>
<span class="comment-title"><?php echo $comment->title; ?></span> —
<?php
}
if ($this->getVar('comment-show-homepage') == 1) {
?>
<a class="author-homepage" href="<?php echo $comment->homepage; ?>" rel="nofollow" title="<?php echo $comment->author; ?>"><?php echo $comment->author; ?></a>
<?php
} else {
?>
<span class="comment-author"><?php echo $comment->author?></span>
<?php
}
?>
<span class="comment-date"><?php echo JCommentsText::formatDate($comment->datetime, JText::_('DATETIME_FORMAT')); ?></span>