OpenBSD falls back to "C" when using an incorrect input with setlocale()
and LC_CTYPE, causing this test, introduced by 008cf040, to fail.  This
removes the culprit test to avoid the portability issue.

Per report from Robert Haas, via buildfarm member curculio.

Discussion: https://postgr.es/m/CA+TgmoZ6ddh3mHD9gU8DvNYoFmuJaYYn1+4AvZNp25vTdRwCAQ@mail.gmail.com
Backpatch-through: 11