Remove unnecessary usage of Serializable to fix a permission issue.

This are the only 2 places where we use Serializable and a headless server log file contained exactly 2 permission violations about Serializable.

See post from @Cervator  in this forum thread: forum.terasology.org/threads/terasology-server-crash-issue-with-log-file.1166/

The other permission issues from that thread get addressed in:
* https://github.com/Terasology/WoodAndStone/pull/29