At some point while setting up the utils subdirectory, I apparently
only got half way through renaming miscucs.c to dup_mb_to_wc.c: I
created the new copy of the file, but I didn't delete the old one, I
didn't mention it in utils/CMakeLists.txt, and I didn't change the
comment at the top.
Now done all three, so we now have just one copy of this utility
module.