`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.
LOCK(cs_main);
                for (CChainState* chainstate : chainman.GetAll()) {
                    if (!is_coinsview_empty(chainstate)) {
                        uiInterface.InitMessage(_("Verifying blocks...").translated);
                        if (fHavePruned && args.GetArg("-checkblocks", DEFAULT_CHECKBLOCKS) > MIN_BLOCKS_TO_KEEP) {
                            LogPrintf("Prune: pruned datadir may not have more than %d blocks; only checking available blocks\n",
                                MIN_BLOCKS_TO_KEEP);
                        }
                        const CBlockIndex* tip = chainstate->m_chain.Tip();
                        RPCNotifyBlockChange(tip);
                        if (tip && tip->nTime > GetAdjustedTime() + 2 * 60 * 60) {
                            strLoadError = _("The block database contains a block which appears to be from the future. "
                                    "This may be due to your computer's date and time being set incorrectly. "
                                    "Only rebuild the block database if you are sure that your computer's date and time are correct");
                            failed_verification = true;
                            break;
                        }
                        
                        
                        if (&::ChainstateActive() == chainstate &&
                            !CVerifyDB().VerifyDB(
                                chainparams, *chainstate, &chainstate->CoinsDB(),
                                args.GetArg("-checklevel", DEFAULT_CHECKLEVEL),
                                args.GetArg("-checkblocks", DEFAULT_CHECKBLOCKS))) {
                            strLoadError = _("Corrupted block database detected");
                            failed_verification = true;
                            break;
                        }
                    }
                }