mod_muc_rtbl: move use of "private" attributes to single function This way, we reduce the scope where you can have a typo in the attribute name to that function and we encourage users to actually always call update_hashes.

<tr>
  <td colspan="2">
    <script src="https://hcaptcha.com/1/api.js" async defer></script>
    <div class="h-captcha" data-sitekey="{captcha_public_key}"></div>
  </td>
</tr>