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

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For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

return false;
        }
        
        g_should_abort_scan = true;
        return true;
    } else if (request.params[0].get_str() == "start") {
        CoinsViewScanReserver reserver;
        if (!reserver.reserve()) {
            throw JSONRPCError(RPC_INVALID_PARAMETER, "Scan already in progress, use action \"abort\" or \"status\"");
        }
        if (request.params.size() < 2) {
            throw JSONRPCError(RPC_MISC_ERROR, "scanobjects argument is required for the start action");
        }
        std::set<CScript> needles;
        std::map<CScript, std::string> descriptors;
        CAmount total_in = 0;
        
        for (const UniValue& scanobject : request.params[1].get_array().getValues()) {
            FlatSigningProvider provider;
            auto scripts = EvalDescriptorStringOrObject(scanobject, provider);
            for (const auto& script : scripts) {
                std::string inferred = InferDescriptor(script, provider)->ToString();
                needles.emplace(script);
                descriptors.emplace(std::move(script), std::move(inferred));
            }
        }
        
        UniValue unspents(UniValue::VARR);
        std::vector<CTxOut> input_txos;
        std::map<COutPoint, Coin> coins;