short getBlobRecordVersion() {
    return blobRecordVersion;
  }
For the message at readSetIndex, does the following:
   1. Reads the whole blob and does a crc check. If the crc check fails, returns null - this means that the record
   is not retrievable anyway.
   2. Adds to a hard delete replacement write set.
   3. Returns the hard delete info.
ambry-messageformat/src/main/java/com/github/ambry/messageformat/BlobStoreHardDelete.java