Show the reset button only when facets are active

test.php

<script>

(function($) {
  $(document).on('facetwp-loaded', function() {
    var in_use = ('' != FWP.build_query_string());
    $('.your-reset-btn').toggleClass('hidden', ! in_use);
  });
})(jQuery);

</script>

<style>
/* add to your stylesheet */
.hidden { display: none; }
</style>