media: docs: get rid of obsoleted udev documentation

This file is very old, and doesn't match the current udev
behavior.

I wanted to preserve it, because we'll need some udev
description some day about how to keep names unique,
but there's nothing here to help with that...

So, be it: let's just discard this document, as it doesn't
provide anything useful anymore.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>