Kill gdata (again)

gdata is currently being used by 3 APIs:

- Contacts API https://developers.google.com/people/contacts-api-migration
- Email Audit API https://developers.google.com/admin-sdk/email-audit/overview
- Classic Sites API https://developers.google.com/sites/docs/1.0/developers_guide_protocol

each of these is in various states of deprecation and ideally we'd remove the gdata code from GAM because it's old, crufty and may have some security issues.

In the case of Contacts API, it's been replaced with the People API. @taers232c are you aware of any use cases where Contacts API is still needed?

In the case of Email Audit API, Google Vault is meant as the much more robust replacement but the Email Audit API is still used by some customers and was never turned down. For this I suggest we drop support from the current GAM release but customers wishing to use Email Audit API calls can continue to run old versions of GAM. Should something break we can always do a patch release to that old version.

In the case of Classic sites API, afaik Classic Sites is entirely turned down: https://workspaceupdates.googleblog.com/2022/11/migrate-classic-google-sites-by-january-30-2023.html @taers232c are you aware of any further usage / need for Classic Sites API?

Once we can replace / remove these 3 APIs we can cleanup the gdata folder(s) and eliminate a lot of crufty old code.