`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.
#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif
#include <init.h>
#include <addrman.h>
#include <amount.h>
#include <banman.h>
#include <blockfilter.h>
#include <chain.h>
#include <chainparams.h>
#include <compat/sanity.h>
#include <fs.h>
#include <hash.h>
#include <httprpc.h>
#include <httpserver.h>
#include <index/blockfilterindex.h>
#include <index/coinstatsindex.h>
#include <index/txindex.h>
#include <init/common.h>
#include <interfaces/chain.h>