Remove a few unreferenced config.h defines.

Remove a few unreferenced config.h defines.

Found by looking through the output of

  for f in $(grep -o '\bHAVE_[A-Z0-9_]*\b' llvm/cmake/config-ix.cmake); do
    echo $f $(git grep $f '*' | wc -l);
  done

in the monorepo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328957 91177308-0d34-0410-b5e6-96231b3b80d8