scripts: sphinx-pre-install: remove Scientific Linux

scripts: sphinx-pre-install: remove Scientific Linux

According with its website: https://scientificlinux.org/

Scientific Linux reached end of life in June 30, 2024.
Also, it was based on RHEL 7, which is not compatible with
our build system anymore.

So, drop support for it.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/dde5e0c95017022840f8a522ce44759e51f52aa1.1754992972.git.mchehab+huawei@kernel.org