scripts: sphinx-pre-install: fix a dependency hint with Ubuntu 16.04

Avoid the scripts to keep asking to install fonts-noto-cjk
on Ubuntu 16.04.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/912b664a8ca54e8c5c5767c3fe9171973eeddd6b.1586883286.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>