FileSpan addDeleteEntry(MockId idToDelete) throws StoreException {
    return addDeleteEntry(idToDelete, null);
  }
Adds a delete entry in the index (real and reference) for {@code idToDelete}.
@param idToDelete the id to be deleted.
@return the {@link FileSpan} of the added entries.
@throws StoreException
ambry-store/src/test/java/com/github/ambry/store/CuratedLogIndexState.java