Doc: clean up some issues with spellings of contributor names.

In the v12 contributors list, remove a couple of duplicates
that had crept in due to variant spellings of a person's name.
Try to standardize Japanese names as given-name-first.

Alexander Lakhin

Discussion: https://postgr.es/m/a8263c91-6a21-61d4-3156-34bf2fe54e15@gmail.com