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{"getmempoolentry",
                "\nReturns mempool data for given transaction\n",
                {
                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id (must be in mempool)"},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "", MempoolEntryDescription()},
                RPCExamples{
                    HelpExampleCli("getmempoolentry", "\"mytxid\"")
            + HelpExampleRpc("getmempoolentry", "\"mytxid\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    uint256 hash = ParseHashV(request.params[0], "parameter 1");
    const CTxMemPool& mempool = EnsureAnyMemPool(request.context);
    LOCK(mempool.cs);
    CTxMemPool::txiter it = mempool.mapTx.find(hash);
    if (it == mempool.mapTx.end()) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Transaction not in mempool");
    }
    const CTxMemPoolEntry &e = *it;
    UniValue info(UniValue::VOBJ);
    entryToJSON(mempool, info, e);
    return info;
},
    };
}
static RPCHelpMan getblockhash()