You can open the file: ROOT/plugins/system/jasocial_feed/jasocial_feed.php
At approx line 503, comment / remove this snippet of code:
$post['source_content'] .= '
<div class="content-links">
<ol class="nav">
<li class="content-links-a">
<a href="https://www.facebook.com/'.$fbid.'/posts/'.preg_replace('/[0-9]+_/','',$dt->id).'" target="_blank" rel="nofollow">'.$srcTxt.'</a>
</li>
<li class="content-links-b">
';
$post['source_content'] .= $dt->link ? '<a href="'.$dt->link.'" target="_blank" rel="nofollow">'.$domain['host'].'</a>' : '';
$post['source_content'] .= ' </li></ol></div>';
Remember to backup this file first.
Then go to backend settings of this plugin and import content again.