Remove duplicate names.

The removed names also appear as:
Andrés García, François Charlier, Gökhan Şengün, Michał Górny, Sébastien
Willemijns, Christopher Conroy, John E. Malmberg, Luca Altea, Peter Su,
S. Moonesamy, Samuel Listopad, Yasuharu Yamada, Karl Moerder
THANKS: added missing contributor from 2012
contributors.sh: filter common alternative name spellings

docs/THANKS-filter is a new filter file for converting contributor names
we get or have recorded in alternative formats to the one we already use
in THANKS. To help us show individual contributors using a single
presentation of their names.