I have to be honest and say I’ve never seen a ‘footer’ on a Wall even though it has a module for it (but no footer position). Nor a Joomla copyright! If you’re showing it you must have it somewhere! 🙂
I’ve just unpacked a quickstart and there is the file in mydomain.com//language/en-GB/en-GB.mod_footer.ini.
You can try to see if this works – untested though. I’m not running a live Wall – so don’t know the results.
mydomain.com/modules/mod_footer/tmpl and edit the default.php line 14
<div class="footer2<?php echo $moduleclass_sfx ?>"><?php echo JText::_('MOD_FOOTER_LINE2'); ?></div>
and delete it or edit it out.
Apart from that I can’t help you I’m afraid!