Get rid of translation strings that only contain punctuation

(Follow-on work from [1])

We've got a few parts of the code that translate strings that contain
only a single punctuation character. I'm not a translator, but I
suspect that these would be tricky to deal with as such short strings
could be used for various different things, and if the required
translation was to differ between requirements, then you're out of
luck.

I looked at: git grep -A 1 "msgid \", \"" and I see French is the only
translation to do anything different with the ", " string, and only in
psql.

src/bin/psql/po/fr.po:msgid ", "
src/bin/psql/po/fr.po-msgstr " , "

This is used for suffixing "unique" or "unique nulls not distinct". I
adjusted the logic there to get rid of the short translation string.

Quite a few are new to v19: fd366065e (AmitK), 48efefa6c (AmitK),
0fc33b005 (PeterE)
The relation.c one is from v18: 8fcd80258 (AmitK)
The describe.c one is from v15: 94aa7cc5f (PeterE)

Should we get rid of these?

David

[1] https://postgr.es/m/CAApHDvohYOdrvhVxXzCJNX_GYMSWBfjTTtB6hgDauEtZ8Nar2A@mail.gmail.com