Don't serialize version when sending through charm

[nilsvu]

We version some classes for serializing them to disk, but we don't need to do this when sending messages within a program through charm. There might be a mechanism in charm to indicate whether serialization is done for writing to disk or for messages, which we could use to avoid sending the version in messages: https://charm.readthedocs.io/en/latest/charm++/manual.html#pup-modes