Filter a custom taxonomy from displaying a button all other taxonomies can show

I think you could use the has_term conditional here, like so:

<?php if( !has_term( 'tax1', 'supplier' ) ) { ?>
    <a href="https://wordpress.stackexchange.com/questions/245515/<?php echo get_post_meta($post->ID,"ecpt_tds', true); ?>">Download Button</a>
<?php } ?>