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.

{
                    {RPCResult::Type::ELISION, "", "Same output as verbosity = 1"},
                    {RPCResult::Type::ARR, "tx", "",
                    {
                        {RPCResult::Type::OBJ, "", "",
                        {
                            {RPCResult::Type::ELISION, "", "The transactions in the format of the getrawtransaction RPC. Different from verbosity = 1 \"tx\" result"},
                            {RPCResult::Type::NUM, "fee", "The transaction fee in " + CURRENCY_UNIT + ", omitted if block undo data is not available"},
                        }},
                    }},
                }},
        },
                RPCExamples{
                    HelpExampleCli("getblock", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\"")
            + HelpExampleRpc("getblock", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    uint256 hash(ParseHashV(request.params[0], "blockhash"));
    int verbosity = 1;
    if (!request.params[1].isNull()) {
        if (request.params[1].isBool()) {
            verbosity = request.params[1].get_bool() ? 1 : 0;
        } else {
            verbosity = request.params[1].get_int();
        }
    }
    CBlock block;
    const CBlockIndex* pblockindex;
    const CBlockIndex* tip;