Slim Cardano.Api.Certificate.Internal to pool-only definitions
Strip the deprecated legacy `Certificate era` GADT, its `ShelleyRelatedCertificate`/`ConwayCertificate` constructors, every `make*Certificate` constructor function, every `*Requirements` GADT, `selectStakeCredentialWitness`, `toShelleyCertificate`, `fromShelleyCertificate`, `isDRepRegOrUpdateCert`, and the legacy `AnchorDataFromCertificateError` + `getAnchorDataFromCertificate`. The module is now responsible only for the (non-deprecated) pool parameter types and their conversion helpers. Update consumers: - `Sign.hs` re-exports `AsTxId` by importing it directly from `Cardano.Api.Tx.Internal.TxIn` (the previous re-export chain went through the legacy `AsType (AsCertificate, AsTxId)` in Internal). The `-Wno-deprecations` pragma is dropped because no deprecated symbol remains. - `Body.hs` and `Certificate/Internal/OperationalCertificate.hs` drop their `Cardano.Api.Certificate.Internal` imports, which became unused once the legacy surface was removed.