docs: pdfdocs: Move CJK monospace font setting to main conf.py

As LaTeX macros for CJK font settings can have Latin-script font
settings as well, settings under Documentation/translations/ can
be moved to the main conf.py.

By this change, translations.pdf built by top-level "make pdfdocs"
can have properly aligned ascii-art diagrams except for Korean
ones.

For the reason of remaining misalignment in Korean diagrams, see
changelog of commit a90dad8f

 ("docs: pdfdocs: Add conf.py
local to translations for ascii-art alignment").

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/eb87790a-03f4-9f29-c8a3-ef2c3e78ca18@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>