`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 <flatfile.h>
#include <hash.h>
#include <index/blockfilterindex.h>
#include <index/txindex.h>
#include <logging.h>
#include <logging/timer.h>
#include <node/blockstorage.h>
#include <node/coinstats.h>
#include <node/ui_interface.h>
#include <policy/policy.h>
#include <policy/settings.h>
#include <pow.h>
#include <primitives/block.h>
#include <primitives/transaction.h>
#include <random.h>
#include <reverse_iterator.h>
#include <script/script.h>
#include <script/sigcache.h>
#include <shutdown.h>
#include <signet.h>
#include <timedata.h>
#include <tinyformat.h>
#include <txdb.h>
#include <txmempool.h>
#include <uint256.h>
#include <undo.h>
#include <util/check.h> 
#include <util/moneystr.h>
#include <util/rbf.h>
#include <util/strencodings.h>