Remove outdated encoding/decoding from the `catalyst-voting` crate

[stanislav-tkach]

Currently all the types in the catalyst-voting crate implement "manual" encoding/decoding providing the to_bytes and from_bytes methods. We should use CBOR encoding instead. It was already partially added by the #705 pull request. When we have CBOR implementation for all of the types then the outdated implementation should be removed completely.