pgsql: Remove dead generators for cyrillic encoding conversion tables

Remove dead generators for cyrillic encoding conversion tables

These tools were used to read the koi-iso.tab, koi-win.tab, and
koi-alt.tab files, which contained the mappings between the
single-byte cyrillic encodings. However, those data files were removed
in commit 4c3c8c048d, back in 2003. These code generators have been
unused and unusable ever since.

The generated tables live in cyrillic_and_mic.c. There has been one
change to the tables since they were generated in 1999, in commit
f4b7624eb07a. So if we resurrected the original data tables, that
change would need to be taken into account.

So this code is very dead. The tables in cyrillic_and_mic.c, which
were originally generated by these tools, are now the authoritative
source for these mappings.

Reviewed-by: Tom Lane, Aleksander Alekseev
Discussion: https://www.postgresql.org/message-id/flat/a821c3dc-36ec-4cee-8b41-7ccaa17adb18@iki.fi

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/679f940740f42f2401f72a6b95dc02b9c0ab3f30

Modified Files
--------------
src/backend/utils/mb/README    |  3 --
src/backend/utils/mb/iso.c     | 74 ------------------------------------------
src/backend/utils/mb/win1251.c | 74 ------------------------------------------
src/backend/utils/mb/win866.c  | 74 ------------------------------------------
4 files changed, 225 deletions(-)