Bug 28386: Remove unknown authors

Bug 28386: Remove unknown authors

Those 3 authors are not in the git history, we should remove them from
the author list.
However we could re-add them to the contributor list with a note saying
for instance they were part of the Catalyst Academy (need to double
check that first)

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 6a701b363fe807389c49358c43bc33d61282e685)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>