one easy way would be to go to ato->Style & configure COMMENTS->Comments Are Closed text and blank out the option. However this would effect All places where the comments are closed, posts as well.
A more elegant way would be to change the option value to
HTML Code:
<p class="comment_closed">Comments are closed.</p>
then add a CSS Insert
HTML Code:
body.page p.comment_closed {display:none;}