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{"verifychain",
                "\nVerifies blockchain database.\n",
                {
                    {"checklevel", RPCArg::Type::NUM, RPCArg::DefaultHint{strprintf("%d, range=0-4", DEFAULT_CHECKLEVEL)},
                        strprintf("How thorough the block verification is:\n%s", MakeUnorderedList(CHECKLEVEL_DOC))},
                    {"nblocks", RPCArg::Type::NUM, RPCArg::DefaultHint{strprintf("%d, 0=all", DEFAULT_CHECKBLOCKS)}, "The number of blocks to check."},
                },
                RPCResult{
                    RPCResult::Type::BOOL, "", "Verified or not"},
                RPCExamples{
                    HelpExampleCli("verifychain", "")
            + HelpExampleRpc("verifychain", "")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    const int check_level(request.params[0].isNull() ? DEFAULT_CHECKLEVEL : request.params[0].get_int());
    const int check_depth{request.params[1].isNull() ? DEFAULT_CHECKBLOCKS : request.params[1].get_int()};
    ChainstateManager& chainman = EnsureAnyChainman(request.context);
    LOCK(cs_main);
    CChainState& active_chainstate = chainman.ActiveChainstate();
    return CVerifyDB().VerifyDB(
        active_chainstate, Params(), active_chainstate.CoinsTip(), check_level, check_depth);
},
    };
}
static void SoftForkDescPushBack(const CBlockIndex* active_chain_tip, UniValue& softforks, const Consensus::Params& params, Consensus::BuriedDeployment dep)