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.

int64_t total_weight = 0;
    int64_t utxo_size_inc = 0;
    std::vector<CAmount> fee_array;
    std::vector<std::pair<CAmount, int64_t>> feerate_array;
    std::vector<int64_t> txsize_array;
    for (size_t i = 0; i < block.vtx.size(); ++i) {
        const auto& tx = block.vtx.at(i);
        outputs += tx->vout.size();
        CAmount tx_total_out = 0;
        if (loop_outputs) {
            for (const CTxOut& out : tx->vout) {
                tx_total_out += out.nValue;
                utxo_size_inc += GetSerializeSize(out, PROTOCOL_VERSION) + PER_UTXO_OVERHEAD;
            }
        }
        if (tx->IsCoinBase()) {
            continue;
        }
        inputs += tx->vin.size(); 
        total_out += tx_total_out; 
        int64_t tx_size = 0;
        if (do_calculate_size) {
            tx_size = tx->GetTotalSize();
            if (do_mediantxsize) {
                txsize_array.push_back(tx_size);
            }
            maxtxsize = std::max(maxtxsize, tx_size);
            mintxsize = std::min(mintxsize, tx_size);
            total_size += tx_size;
        }