Rename rlp::decode_vector to decode

[yperbasis]

For consistency's sake. Then we can remove functions like

template <>
rlp::DecodingResult decode(ByteView& from, BlockBodiesPacket& to) noexcept {
    return rlp::decode_vector(from, to);
}

[AndreaLanfranchi]

@yperbasis can we close this ?

[yperbasis]

@AndreaLanfranchi Nope because it's not done yet :)