message: dcsctp: remove unused WritePacketHeader method
  Cr-Commit-Position: refs/heads/master@{#34712}
diff: @@ -77,7 +77,6 @@ class SctpPacket {
  std::vector<uint8_t> Build();
  private:
  - void WritePacketHeader();
  VerificationTag verification_tag_;
  uint16_t source_port_;
  uint16_t dest_port_;
  