add changelog and update migration docs

CHANGELOG.md

@@ -52,6 +52,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (testing) [\#6070](https://github.com/cosmos/ibc-go/pull/6070) Remove `AssertEventsLegacy` function.
 * (core) [\#6138](https://github.com/cosmos/ibc-go/pull/6138) Remove `Router` reference from IBC core keeper and use instead the router on the existing `PortKeeper` reference.
 * (core/04-channel) [\#6023](https://github.com/cosmos/ibc-go/pull/6023) Remove emission of non-hexlified event attributes `packet_data` and `packet_ack`.
+* (core) [\#6320][https://github.com/cosmos/ibc-go/pull/6320] Remove unnecessary `Proof` interface from `exported` package.
 
 ### State Machine Breaking
 

docs/docs/05-migrations/13-v8-to-v9.md

@@ -28,6 +28,7 @@ There are four sections based on the four potential user groups of this document
 
 The `exported.ChannelI` and `exported.CounterpartyChannelI` interfaces have been removed. Please use the concrete types.
 The `exported.ConnectionI` and `exported.CounterpartyConnectionI` interfaces have been removed. Please use the concrete types.
+The `exported.Proof` interface has been removed. Please use the `MerkleProof` concrete type.
 
 The functions `GetState()`, `GetOrdering()`, `GetCounterparty()`, `GetConnectionHops()`, `GetVersion()` of the `Channel` type have been removed.
 The functions `GetPortID()`, `GetChannelID()` of the `CounterpartyChannel` type have been removed.