message: drop unused item and index for placeholders
diff: {{#if loadItemsTask.isRunning}}
  {{#if (and usePlaceholders placeholderCount)}}
  <ul class="list-group m-md">
  - {{#each (range 1 placeholderCount) as |item index|}}
  + {{#each (range 1 placeholderCount)}}
  {{yield (hash
  - placeholder=(component 'paginated-relation/x-item' item=item index=index)
  + placeholder=(component 'paginated-relation/x-item')
  )}}
  {{/each}}
  </ul>
  