Hello Andrew.

You can remove this code from ...\components\com_easydiscuss\themes\flatt\post.vote.php at line 43 until line 47

	<?php if( $access->canVote() && !$post->isVoted ){ ?>

		<a href="javascript:void(0);" class="vote-down voteDown"> <i class="icon-minus-sign"></i></a>

	<?php }else{ ?>

		<a href="javascript:void(0);" class="vote-down" <?php if( $system->my->id ){ ?> data-original-title="<?php echo JText::_( 'COM_EASYDISCUSS_ALREADY_VOTED_POLL' ); ?>" data-placement="top" rel="ed-tooltip"  <?php } ?>> <i class="icon-minus-sign"></i></a>

	<?php } ?>

Hope this help