docs/interop: Sanitize QMP reference manuals TOC

docs/interop: Sanitize QMP reference manuals TOC

The "QEMU QMP Reference Manual" and the "QEMU Storage Daemon QMP
Reference Manual" start with a table of contents that looks like this:

    Contents

    * Title of the manual
      * Title of first first-level section
        * Title of its first second-level section
        * Title of its second second-level section
        ...
      * Title of second first-level section
      ...

The first level is useless.  Drop it.

While there, delete the option that limits the TOC to depth 3.  Its
actual depth was 3 before the patch, and is now 2.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20250404121413.1743790-5-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>