ctests: invert a utf8x test failing on TL23

ctests: invert a utf8x test failing on TL23

It seems that utf8x is not supported, or needed, on updated TL. From
David Carlisle:

  utf8x by default does nothing now, but as a compromise
  compatibility for some specific existing documents if you
  explicitly load ucs then it and utf8x work as before, but that
  over writes all of latex's default unicode handling and things
  will go wrong. There really isn't much that can be said other than
  don't load the package. The alternative would be to make ucs do
  nothing as well, but that would stop some documents working that
  currently work.