`banlist.dat` was introduced in https://github.com/bitcoin/bitcoin/pull/6310, storing nodes that were automatically banned (due to exceeding the misbehavior threshold) and manually banned (through the `setban` RPC).

Automatic bans were removed in https://github.com/bitcoin/bitcoin/pull/19219 and replaced with a discouragement filter. That filter is not saved to disk/persisted over shutdown/startup. The `banlist.dat` therefore now only contains addresses that have been banned through the `setban` rpc.

Since https://github.com/bitcoin/bitcoin/pull/15935, we have a specific file for configuration that is updated through the RPC and persisted over shutdown/startup, namely `settings.json`. We should therefore move the manual ban configuration from `banlist.dat` to `settings.json`. Doing so has a couple of benefits:

- `settings.json` is human readable and easily analyzable by any json parser.
- we wouldn't need to maintain custom [de]serialization code for the `banlist.dat` file.

`banlist.dat` is expected to be fairly small and infrequently updated, so disk space/performance are not huge concerns.
chainstate->InitCoinsCache(nCoinCacheUsage);
                    assert(chainstate->CanFlushToDisk());
                    if (!is_coinsview_empty(chainstate)) {
                         
                        if (!chainstate->LoadChainTip(chainparams)) {
                            strLoadError = _("Error initializing block database");
                            failed_chainstate_init = true;
                            break;  
                        }
                        assert(chainstate->m_chain.Tip() != nullptr);
                    }
                }
                if (failed_chainstate_init) {
                    break;  
                }
            } catch (const std::exception& e) {
                LogPrintf("%s\n", e.what());
                strLoadError = _("Error opening block database");
                break;
            }
            if (!fReset) {
                LOCK(cs_main);
                auto chainstates{chainman.GetAll()};
                if (std::any_of(chainstates.begin(), chainstates.end(),
                                [&chainparams](const CChainState* cs) EXCLUSIVE_LOCKS_REQUIRED(cs_main) { return cs->NeedsRedownload(chainparams); })) {
                    strLoadError = strprintf(_("Witness data for blocks after height %d requires validation. Please restart with -reindex."),
                                             chainparams.GetConsensus().SegwitHeight);
                    break;
                }
            }