Add changelog fragment for legacy Certificate removal

Author: Jimbo4350

.changes/20260515_cardano_api_remove_legacy_certificate_type.yml

@@ -0,0 +1,8 @@
+project: cardano-api
+pr: 1210
+kind:
+  - breaking
+description: |
+  Remove the deprecated `data Certificate era` GADT, its `ShelleyRelatedCertificate`/`ConwayCertificate` constructors, all `make*Certificate` functions, all `*Requirements` GADTs, and the public `Cardano.Api.Certificate` module. Consumers should use the certificate API exposed via `Cardano.Api.Experimental.Certificate` (era-polymorphic, Conway onwards) or `Cardano.Api.Compatible.Certificate` (covers all Shelley-based eras).
+
+  Pool-related types (`PoolId`, `StakePoolParameters`, `StakePoolRelay`, `StakePoolMetadataReference`) and their conversion helpers remain in `Cardano.Api.Certificate.Internal` and are re-exported by `Cardano.Api.Experimental.Certificate`.

.changes/20260515_cardano_wasm_remove_legacy_certificate_type.yml

@@ -0,0 +1,6 @@
+project: cardano-wasm
+pr: 1210
+kind:
+  - maintenance
+description: |
+  Switch the `PoolId` import in `Cardano.Wasm.Api.Certificate.StakeCertificate` from `Cardano.Api` to `Cardano.Api.Experimental.Certificate` after the legacy `Cardano.Api.Certificate` re-export module was removed upstream.