находим 37 строчку, и удаляем:

<label class="formUrl" for="commentURL"><?php echo JText::_('K2_WEBSITE_URL'); ?></label>

<input class="inputbox" type="text" name="commentURL" id="commentURL" value="<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>"  onblur="if(this.value=='') this.value='<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>';" onfocus="if(this.value=='<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>') this.value='';" />