docs: cdrom-standard.rst: get rid of uneeded UTF-8 chars

This file was converted from a LaTeX one. The conversion used
some UTF-8 characters at the literal blocks. Replace them
by normal ASCII characters.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Jens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/79c3f482da17ea48d69b6e6ad1b7fb102b9dd7bf.1620744606.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>