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{"getblockhash",
                "\nReturns hash of block in best-block-chain at height provided.\n",
                {
                    {"height", RPCArg::Type::NUM, RPCArg::Optional::NO, "The height index"},
                },
                RPCResult{
                    RPCResult::Type::STR_HEX, "", "The block hash"},
                RPCExamples{
                    HelpExampleCli("getblockhash", "1000")
            + HelpExampleRpc("getblockhash", "1000")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    ChainstateManager& chainman = EnsureAnyChainman(request.context);
    LOCK(cs_main);
    const CChain& active_chain = chainman.ActiveChain();
    int nHeight = request.params[0].get_int();
    if (nHeight < 0 || nHeight > active_chain.Height())
        throw JSONRPCError(RPC_INVALID_PARAMETER, "Block height out of range");
    CBlockIndex* pblockindex = active_chain[nHeight];
    return pblockindex->GetBlockHash().GetHex();
},
    };
}
static RPCHelpMan getblockheader()