RPCs that return detailed information about mempool entries (e.g. `getmempoolentry` and `getrawmempool(verbose=True)` include the fields `fee`, `modifiedfee`, `descendantfees`, and `ancestorfees` which were marked as "DEPRECATED" and replaced with a `fees` object field in #12240 (since v0.17).

We should remove these fields, but first, properly deprecate them using `-deprecatedrpc`.

#### Useful skills:

- basic understanding of Bitcoin Core RPC interface

#### Want to work on this issue?

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

{
    return RPCHelpMan{"gettxoutsetinfo",
                "\nReturns statistics about the unspent transaction output set.\n"
                "Note this call may take some time if you are not using coinstatsindex.\n",
                {
                    {"hash_type", RPCArg::Type::STR, RPCArg::Default{"hash_serialized_2"}, "Which UTXO set hash should be calculated. Options: 'hash_serialized_2' (the legacy algorithm), 'muhash', 'none'."},
                    {"hash_or_height", RPCArg::Type::NUM, RPCArg::Optional::OMITTED_NAMED_ARG, "The block hash or height of the target height (only available with coinstatsindex).", "", {"", "string or numeric"}},
                    {"use_index", RPCArg::Type::BOOL, RPCArg::Default{true}, "Use coinstatsindex, if available."},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::NUM, "height", "The block height (index) of the returned statistics"},
                        {RPCResult::Type::STR_HEX, "bestblock", "The hash of the block at which these statistics are calculated"},
                        {RPCResult::Type::NUM, "txouts", "The number of unspent transaction outputs"},
                        {RPCResult::Type::NUM, "bogosize", "Database-independent, meaningless metric indicating the UTXO set size"},
                        {RPCResult::Type::STR_HEX, "hash_serialized_2",  true, "The serialized hash (only present if 'hash_serialized_2' hash_type is chosen)"},
                        {RPCResult::Type::STR_HEX, "muhash",  true, "The serialized hash (only present if 'muhash' hash_type is chosen)"},
                        {RPCResult::Type::NUM, "transactions",  true, "The number of transactions with unspent outputs (not available when coinstatsindex is used)"},
                        {RPCResult::Type::NUM, "disk_size",  true, "The estimated size of the chainstate on disk (not available when coinstatsindex is used)"},
                        {RPCResult::Type::STR_AMOUNT, "total_amount", "The total amount of coins in the UTXO set"},
                        {RPCResult::Type::STR_AMOUNT, "total_unspendable_amount",  true, "The total amount of coins permanently excluded from the UTXO set (only available if coinstatsindex is used)"},