Get rid of /eventStats endpoint + /family-tokens collection

[fcamblor]

In profit to /publicEventStats endpoint which provides multiple kind of accesses based on /public-token/ tokens

We will need to ensure every consumers of /publicEventStats (devoxx CFP mainly) stopped calling us prior to removing the endpoint

[fcamblor]

@stephanj told me this event was no longer called from cfp.dev, we should be free to remove it

This makes me wonder if /family-token shouldn't be removed after that (the only remaining place where we might use it is on /attendeesFeedbacks and we might refactor it to use public-tokens instead)

[fcamblor]

Provided replacement APIs for GET /publicEventStats (splitted into GET /events/:eventId/topTalks and GET /events/:eventId/talksStats) and proposed a MR to CFP.dev implementation to get rid of this endpoint and replace it with new endpoints.
This MR has presently been merged, released (2.13.0) and deployed on every cfp.dev 2024 instances.

There is only 1 remaining caller still relying on /publicEventStats: SocialWallFX project (for displaying top talks on Devoxx BE and VoxxedDays Zurich
I contacted SocialWallFX developers to ask them to migrated to new endpoint when possible.

[fcamblor]

Note that family tokens should not longer be used (main user of these tokens was cfp.dev)

[fcamblor]

fixed deletion of family-event-tokens collection