Remove hide and print flag fields from events endpoint

From #555 — see description in comment at https://github.com/shift-org/shift-docs/issues/555#issuecomment-1892683221.

These fields aren't needed in the public read-only events endpoint:

• hideemail
• hidephone
• hidecontact
• printemail
• printphone
• printweburl
• printcontact

They should still be accepted and sent in the manage_event and retrieve_event endpoints.

Also, we should keep the print title and print description fields in the events endpoint response, at least for now. We currently use those in the calendar grid view and the iCal feed. We may revisit that eventually, but their current usage is different than these boolean flag fields.