Referendum 18 was to open the Moonriver <> Mangata X channel using the whitelisted track in order to accelerate the deployment.  However, it was set up with an incorrect parameter which would cause an XCM version mismatch.

Referendum 19 is to replace 18 and this referendum (#20) is to cancel #18.

Cancel an ongoing referendum.

- `origin`: must be the `CancelOrigin`.
- `index`: The index of the referendum to be cancelled.

Emits `Cancelled`.

- **Problem Statement:** Ongoing costs for supporting Moonbeam, Moonriver, and Moonbase alpha networks in BlastAPI, requested quarterly for Q1 2024.
- **Significance:** Ensuring easy, fast, and reliable access to high-performance APIs for Moonbeam, Moonriver, and Moonbase alpha networks, allowing developers to focus on app development without infrastructure concerns.
- **Proposed Solution:** Utilizing $13500 for Q1 2024 to support Moonbeam, Moonriver, and Moonbase alpha nodes, covering infrastructure costs and maintenance.
- **Expected Outcomes:** Enhanced service with RPC and Websockets APIs, 99.9% availability, 24/7 monitoring, developer support, and multi-region hosting, promoting decentralized third-party node participation and rewards.

#20 Cancel Referendum 18 due to incorrect parameter