Avoid using non-ASCII commentary in daitch_mokotoff.c.

Avoid using non-ASCII commentary in daitch_mokotoff.c.

Commit d6b5dee42 failed to suppress that warning from MSVC,
so let's just get rid of all non-ASCII glyphs in the comments.
The comment for iso8859_1_to_ascii_upper[] is not essential,
and the other cases can be handled by spelling out the
Unicode character names.

(I'm now really in the dark as to why MSVC doesn't complain
about predicate.c's comment.  But whatever.)

Discussion: https://postgr.es/m/1546512.1681495035@sss.pgh.pa.us