articles/contributors: Move keramida to the Development Team Alumni

Missed entry in time; dates came from:
https://cgit.freebsd.org/doc/commit/?id=e8a9a5be4956739f3fd1f8d50a4b6bf5aeba5428
https://cgit.freebsd.org/doc/commit/?h=internal/admin&id=a50eb5c4872a34252c9cf9d2a95ad79e86b5ab70