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.

cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&height]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height >= height || !IsRPCRunning();});
        else
            cond_blockchange.wait(lock, [&height]() EXCLUSIVE_LOCKS_REQUIRED(cs_blockchange) {return latestblock.height >= height || !IsRPCRunning(); });
        block = latestblock;
    }
    UniValue ret(UniValue::VOBJ);
    ret.pushKV("hash", block.hash.GetHex());
    ret.pushKV("height", block.height);
    return ret;
},
    };
}
static RPCHelpMan syncwithvalidationinterfacequeue()
{
    return RPCHelpMan{"syncwithvalidationinterfacequeue",
                "\nWaits for the validation interface queue to catch up on everything that was there when we entered this function.\n",
                {},
                RPCResult{RPCResult::Type::NONE, "", ""},
                RPCExamples{
                    HelpExampleCli("syncwithvalidationinterfacequeue","")
            + HelpExampleRpc("syncwithvalidationinterfacequeue","")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    SyncWithValidationInterfaceQueue();
    return NullUniValue;
},
    };
}
static RPCHelpMan getdifficulty()