In the menu.php file inside of CSSMenuWriter > cssmw you can just remove line 25, it looks like this:
25: <li><span><a href="<?php echo($assumedRoot); ?>admin/contents_insert.php">Insert New Content</a></span></li>
You can also comment it out but you would need to use a regular html comment like this:
25: <!--<li><span><a href="<?php echo($assumedRoot); ?>admin/contents_insert.php">Insert New Content</a></span></li>-->