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

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{
    return RPCHelpMan{
        "dumptxoutset",
        "\nWrite the serialized UTXO set to disk.\n",
        {
            {"path",
                RPCArg::Type::STR,
                RPCArg::Optional::NO,
                 "",
                "path to the output file. If relative, will be prefixed by datadir."},
        },
        RPCResult{
            RPCResult::Type::OBJ, "", "",
                {
                    {RPCResult::Type::NUM, "coins_written", "the number of coins written in the snapshot"},
                    {RPCResult::Type::STR_HEX, "base_hash", "the hash of the base of the snapshot"},
                    {RPCResult::Type::NUM, "base_height", "the height of the base of the snapshot"},
                    {RPCResult::Type::STR, "path", "the absolute path that the snapshot was written to"},
                    {RPCResult::Type::STR_HEX, "txoutset_hash", "the hash of the UTXO set contents"},