message: fix compilation issue related the certificate change and stake change merge.
diff: @@ -12,7 +12,6 @@ pub struct SignatureRaw(Vec<u8>);
  impl property::Serialize for SignatureRaw {
  type Error = std::io::Error;
  fn serialize<W: std::io::Write>(&self, mut writer: W) -> Result<(), Self::Error> {
  - use chain_core::packer::*;
  writer.write_all(self.0.as_ref())?;
  Ok(())
  }
  @@ -29,7 +28,7 @@ pub enum CertificateContent {
  StakeKeyRegistration(StakeKeyRegistration),
  StakeKeyDeregistration(StakeKeyDeregistration),
  StakeDelegation(StakeDelegation),
  - StakePoolRegistration(StakePoolRegistration),
  + StakePoolRegistration(StakePoolInfo),
  StakePoolRetirement(StakePoolRetirement),
  }
  