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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int64_t weight = 0;
        if (do_calculate_weight) {
            weight = GetTransactionWeight(*tx);
            total_weight += weight;
        }
        if (do_calculate_sw && tx->HasWitness()) {
            ++swtxs;
            swtotal_size += tx_size;
            swtotal_weight += weight;
        }
        if (loop_inputs) {
            CAmount tx_total_in = 0;
            const auto& txundo = blockUndo.vtxundo.at(i - 1);
            for (const Coin& coin: txundo.vprevout) {
                const CTxOut& prevoutput = coin.out;
                tx_total_in += prevoutput.nValue;
                utxo_size_inc -= GetSerializeSize(prevoutput, PROTOCOL_VERSION) + PER_UTXO_OVERHEAD;
            }
            CAmount txfee = tx_total_in - tx_total_out;
            CHECK_NONFATAL(MoneyRange(txfee));
            if (do_medianfee) {
                fee_array.push_back(txfee);
            }
            maxfee = std::max(maxfee, txfee);
            minfee = std::min(minfee, txfee);
            totalfee += txfee;
            
            CAmount feerate = weight ? (txfee * WITNESS_SCALE_FACTOR) / weight : 0;
            if (do_feerate_percentiles) {
                feerate_array.emplace_back(std::make_pair(feerate, weight));