Remove hide and print flag fields from events endpoint

[carrythebanner]

From #555 — see description in comment at #555 (comment).

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.

[carrythebanner]

#558 should have made it so that those fields aren't needed in preview mode, but double-check preview mode when making this change to be sure.

[carrythebanner]

Also update CALENDAR_API.md.

[carrythebanner]

See also the published field. I believe this is always true in the public, read-only events endpoint. (If an event isn't published, it isn't included.) Need to make sure there aren't any uncommon uses for it currently (calendar feed?), but on the surface it appears to be needed only by the privileged manage/retrieve endpoints.

See d6df4a4 for when it was added (yes, it was me 🙃).