docs: Remove stale TODO comments about license and version

docs: Remove stale TODO comments about license and version

Since commits 13f934e79fa and 3a50c8f3067aaf, our HTML docs include a
footer to all pages stating the license and version.  We can
therefore delete the TODO comments suggesting we should do that from
our .rst files.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Reviewed-by: Cleber Rosa <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Message-id: 20210722192016[email protected]