Remove duplicate names from CREDITS
- "Michael M." was added manually, "Schnark" came from git log - see
https://phabricator.wikimedia.org/p/Schnark/ for the connection of both
names
- same email address, already in .mailmap
- "victorbarbu" in Ib031bef17c8a7d708a5c7878e74967d19217bbc8
- "Victor Barbu" in I5285dbfc47d6429e16b7e7839bf55d48320d0bf0
- same email address, added to mailmap
- matejsuchanek in I4ef06d781bcb1aa0bc7b6d27c27cfde98390a367
- Matěj Suchánek in Ib888634af281fc2347eaa389db4141782a98c15c
Change-Id: Ibc784dca10c9f74918daf1c3940f3cd17de1deda