pgsql: Remove useless unconstify

Remove useless unconstify

Digging into the history, this was not necessary even when it was
added, but might have been some time before that.  In any case, there
is no use for this now.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/9e43ab3dd79ddb5a6a3f7cdb5b1d6dffc9e7765b

Modified Files
--------------
src/backend/utils/adt/formatting.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)