`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.
#include <rpc/blockchain.h>
#include <rpc/register.h>
#include <rpc/server.h>
#include <rpc/util.h>
#include <scheduler.h>
#include <script/sigcache.h>
#include <script/standard.h>
#include <shutdown.h>
#include <sync.h>
#include <timedata.h>
#include <torcontrol.h>
#include <txdb.h>
#include <txmempool.h>
#include <txorphanage.h>
#include <util/asmap.h>
#include <util/check.h>
#include <util/moneystr.h>
#include <util/string.h>
#include <util/system.h>
#include <util/threadnames.h>
#include <util/translation.h>
#include <validation.h>
#include <validationinterface.h>
#include <walletinitinterface.h>
#include <functional>
#include <set>
#include <stdint.h>
#include <stdio.h>
#include <thread>
#include <vector>