docs: admin: unicode: update information on state of lanana.org document

docs: admin: unicode: update information on state of lanana.org document

Replace link to a non-existing page with a note that lanana.org does not
maintain Linux Zone Unicode Assignments anymore.

Remove the reference to H. Peter Anvin and the unicode lanana.org email as
the maintainer of this file, as at this point, this is all maintained by
the general kernel community.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20230307144000.29539-3-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>