revokeLastDeviceRecoveryKey

Revokes this user's offline recovery key currentKey (docs/recovery-key-lifecycle.md): this device's signed request and currentKey's signature. Afterwards no last-device recovery is possible, and outstanding challenges are dead, until a new key is registered with registerLastDeviceRecoveryKey (the recovery key epoch continues). Nothing is generated as a replacement.

Reads the status first: an already revoked key gives LastDeviceRecoveryKeyRevocationResult.ALREADY_REVOKED without sending anything. Throws SecureMessageClientException.LastDeviceRecoveryKeyNotConfigured if the user never registered a key, SecureMessageClientException.LastDeviceRecoveryKeyMismatch if currentKey is not the active key, and SecureMessageTransportException.RecoveryKeyRevocationRejected if the server refused. Never called implicitly.