`RewindBlockIndex` was made to allow nodes upgrading to new consensus rules post-segwit fork to 
download new consensus data (i.e witnesses) without having to go through a whole IBD. It has been pointed than now really few pre-segwit nodes care to upgrade and that this logic may be irrelevant.

See https://github.com/bitcoin/bitcoin/pull/17737#discussion_r358514335 in review  of #17737 for more context pointers.
_("Error reading from database, shutting down."),
                            "", CClientUIInterface::MSG_ERROR);
                    });
                    
                    
                    if (!chainstate->CoinsDB().Upgrade()) {
                        strLoadError = _("Error upgrading chainstate database");
                        failed_chainstate_init = true;
                        break;
                    }
                    
                    if (!chainstate->ReplayBlocks(chainparams)) {
                        strLoadError = _("Unable to replay blocks. You will need to rebuild the database using -reindex-chainstate.");
                        failed_chainstate_init = true;
                        break;
                    }
                    
                    chainstate->InitCoinsCache(nCoinCacheUsage);
                    assert(chainstate->CanFlushToDisk());
                    if (!is_coinsview_empty(chainstate)) {
                        
                        if (!chainstate->LoadChainTip(chainparams)) {
                            strLoadError = _("Error initializing block database");
                            failed_chainstate_init = true;
                            break; 
                        }
                        assert(chainstate->m_chain.Tip() != nullptr);
                    }
                }
                if (failed_chainstate_init) {