How to remove all menus and navigation from a page?

This can be achieved by duplicating the cloud theme, rename it to what you want and edit theme.php, now remove items like:

  <nav>
   <div id="menu">
    <!-- MENU AREA -->
    <ul id="nav">
     <?php $template->outputMenu() ?>
    </ul>
   </div>
   <!-- BREADCRUMB MENU AREA -->
   <div id="scripticon">
    <?php $template->outputScriptIcon() ?>
   </div>
   <div id="history">
    <ul id="bread">
     <?php $template->outputBreadcrumbs() ?>
    </ul>
   </div>
  </nav>

And
    <div id="info">
    <div id="logindetail">
     <?php $template->outputLoginLink() ?>
     &#44;&nbsp;
     <?php $template->outputRole() ?>
     &#44;&nbsp;
     <?php $template->outputGroup() ?>
    </div>
    <div id="datetime">
     <?php $template->outputTime() ?>
    </div>
   </div>

Now just assign your menu item to this new custom theme.