HNSpecial.settings.registerModule("hide_downvote", function () {
  function hideDownvoteButton () {
    var arrows = _.toArray(document.getElementsByClassName('votearrow'));

    arrows.forEach(function(arrow) {
      if (arrow.classList.contains('rotate180')) {
        arrow.parentElement.remove();
      }
    });
  }

  hideDownvoteButton();
});

HNSpecial.settings.registerModule("hide_downvote", function hideDownvotes() {
  var arrows = _.toArray(document.getElementsByClassName('votearrow'));

  arrows.forEach(function(arrow) {
    if (arrow.classList.contains('rotate180')) {
      arrow.parentElement.remove();
    }
  });
});

Remove function definition for brevity