csv: Do not export private user information
We don't need to know about a user's real name, the (hopefully anonymous) serial is enough for our data collection purposes.
I'm only hiding the fields @barbayellow explicitly mentioned to me. However, there seems to be other potentially private informations in other fields, that we probably shouldn't have in CSV exports. Things like the family or marital status, or even the gender.
In any case, those would just need to be added to the new User.PRIVATE_DATA
field, and then they would not be exported to CSVs any more.