Aha, I guess I have a clue. The Wiki module provided its filter in Moodle 1.9 as eg Glossary or Database does. I guess the database of the QA site comes from that times. Then when Wiki 2.0 landed in CVS HEAD (see commit 00710f), the mod/wiki/filter.php was deleted but there was no upgrade step to clear the filter record from the list of registered filters.
So this is actually Wiki 2.x bug and I believe we can safely remove the row from