`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.
CChainState* m_active_chainstate GUARDED_BY(::cs_main) {nullptr};
    
    
    bool m_snapshot_validated{false};
    
    [[nodiscard]] bool PopulateAndValidateSnapshot(
        CChainState& snapshot_chainstate,
        CAutoFile& coins_file,
        const SnapshotMetadata& metadata);
    
    friend CChainState& ChainstateActive();
    friend CChain& ChainActive();
public:
    std::thread m_load_block;
    
    
    BlockManager m_blockman GUARDED_BY(::cs_main);
    
    
    int64_t m_total_coinstip_cache{0};