Remove the menu bar in the documentation or fix all the broken links

Summary

The following links need updating as they all point to a blank page about a Gitlab migration:

• Documentation->wiki
• Documentation->view tickets
• Documentation->new ticket
• Documentation->git repository

  If you have any questions you can find us on our Discord at
   https://www.rtems.org/discord in #gitlab-support for updates

In addition:

• The "Home" button on the top-left corner does not point back to rtems.org but to the documentation itself https://docs.rtems.org/index.html - how should one return to rtems.org?
• The rtems logo does not link back to rtems.org

It seems that the entire navigation bar should be removed.