message: fix: don't link contributors page on tombstone
diff: <div ...attributes>
  <div local-class='Field'>
  <h4>
  + {{#if @extendedFields}}
  <OsfLink
  data-analytics-name='Contributors'
  @href={{concat '/' this.registration.id '/contributors'}}
  >
  {{t 'registries.registration_metadata.contributors'}}
  </OsfLink>
  + {{else}}
  + {{t 'registries.registration_metadata.contributors'}}
  + {{/if}}
  </h4>
  <ContributorList
  @node={{this.registration}}
  