Due to the index encoding error discovered in the 9380 version of `pallet-xcm`, the system parachains will need to be re-released.

Cancel an ongoing referendum.

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

Emits `Cancelled`.

- There was a mistake in the computer program called `pallet-xcm`.
- The mistake made the system not work correctly.
- The parts of the system called parachains will need to be fixed and released again.
- This is because the mistake made them not work properly.
- The people who made the mistake are working to fix it.

#128 Cancel Referendum 127