`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.
#ifndef BITCOIN_VALIDATION_H
#define BITCOIN_VALIDATION_H
#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif
#include <amount.h>
#include <attributes.h>
#include <coins.h>
#include <consensus/validation.h>
#include <crypto/common.h>