Remove custom EncodeScale/DecodeScale once post library updated

[evt]

// Post is an alias to postShared.Proof.
type Post postShared.Proof

// EncodeScale implements scale codec interface.
func (p *Post) EncodeScale(enc *scale.Encoder) (total int, err error) {
	if n, err := scale.EncodeCompact32(enc, uint32(p.Nonce)); err != nil {
		return total, err
	} else { // nolint
		total += n
	}
	if n, err := scale.EncodeByteSlice(enc, p.Indices); err != nil {
		return total, err
	} else { // nolint
		total += n
	}
	return total, nil
}

// DecodeScale implements scale codec interface.
func (p *Post) DecodeScale(dec *scale.Decoder) (total int, err error) {
	if field, n, err := scale.DecodeCompact32(dec); err != nil {
		return total, err
	} else { // nolint
		total += n
		p.Nonce = uint32(field)
	}
	if field, n, err := scale.DecodeByteSlice(dec); err != nil {
		return total, err
	} else { // nolint
		total += n
		p.Indices = field
	}
	return total, nil
}

above EncodeScale/DecodeScale methods should be removed once they're enabled for postShared.Proof