Delete the v2 compatibility routes.

[SamirTalwar]

It seems that no one is using these any more.

[BenoitRanque]

Glad to see this go

[BenoitRanque]

I think we can also remove the dependency on the v2 rust types

[paf31]

This is referenced here: https://hasura.io/docs/3.0/connectors/v2-compatibility

How are we making these decisions to remove features?

[SamirTalwar]

I asked around if anyone was using this and did not get any affirmatives, or anyone pointing out that it's useful. I didn't know about the docs.

Happy to restore them if they're useful. I will put them under a Cargo feature so we can avoid the gdc_rust_types dependency in ndc-postgres, and update the docs accordingly.