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.

{"descriptor", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "An output descriptor"},
                {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with output descriptor and metadata",
                {
                    {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
                    {"range", RPCArg::Type::RANGE, RPCArg::Default{1000}, "The range of HD chain indexes to explore (either end or [begin,end])"},
                }},
            },
                        "[scanobjects,...]"},
        },
        {
            RPCResult{"When action=='abort'", RPCResult::Type::BOOL, "", ""},
            RPCResult{"When action=='status' and no scan is in progress", RPCResult::Type::NONE, "", ""},
            RPCResult{"When action=='status' and scan is in progress", RPCResult::Type::OBJ, "", "",
            {
                {RPCResult::Type::NUM, "progress", "The scan progress"},
            }},
            RPCResult{"When action=='start'", RPCResult::Type::OBJ, "", "", {
                {RPCResult::Type::BOOL, "success", "Whether the scan was completed"},
                {RPCResult::Type::NUM, "txouts", "The number of unspent transaction outputs scanned"},
                {RPCResult::Type::NUM, "height", "The current block height (index)"},
                {RPCResult::Type::STR_HEX, "bestblock", "The hash of the block at the tip of the chain"},
                {RPCResult::Type::ARR, "unspents", "",
                {
                    {RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR_HEX, "txid", "The transaction id"},
                        {RPCResult::Type::NUM, "vout", "The vout value"},
                        {RPCResult::Type::STR_HEX, "scriptPubKey", "The script key"},
                        {RPCResult::Type::STR, "desc", "A specialized descriptor for the matched scriptPubKey"},
                        {RPCResult::Type::STR_AMOUNT, "amount", "The total amount in " + CURRENCY_UNIT + " of the unspent output"},