message: Drop unused fields in aesGCMHKDFReader
diff: @@ -200,16 +200,6 @@ func (d aesGCMHKDFSegmentDecrypter) DecryptSegment(segment, nonce []byte) ([]byt
  // aesGCMHKDFReader works as a wrapper around underlying io.Reader.
  type aesGCMHKDFReader struct {
  *noncebased.Reader
  - aesGCMHKDF *AESGCMHKDF
  - decryptedSegments uint64
  - noncePrefix []byte
  - cipher cipher.AEAD
  - underlyingReader io.Reader
  -
  - pt []byte
  - ptPos int
  - ct []byte
  - ctPos int
  }
  // NewDecryptingReader returns a wrapper around underlying io.Reader, such that
  