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{"getblockcount",
                "\nReturns the height of the most-work fully-validated chain.\n"
                "The genesis block has height 0.\n",
                {},
                RPCResult{
                    RPCResult::Type::NUM, "", "The current block count"},
                RPCExamples{
                    HelpExampleCli("getblockcount", "")
            + HelpExampleRpc("getblockcount", "")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    ChainstateManager& chainman = EnsureAnyChainman(request.context);
    LOCK(cs_main);
    return chainman.ActiveChain().Height();
},
    };
}
static RPCHelpMan getbestblockhash()