[lib/shared] clean RefreshKeyRequest type

Summary:
This is not a separate message type, this is a message sent as a payload of MessageToDevice.

The following change from D10379

Depends on D10510

Test Plan: Rust/Flow

Reviewers: marcin, varun, michal

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10511