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.

{RPCResult{RPCResult::Type::STR_HEX, "transactionid", "parent transaction id"}}},
    RPCResult{RPCResult::Type::ARR, "spentby", "unconfirmed transactions spending outputs from this transaction",
        {RPCResult{RPCResult::Type::STR_HEX, "transactionid", "child transaction id"}}},
    RPCResult{RPCResult::Type::BOOL, "bip125-replaceable", "Whether this transaction could be replaced due to BIP125 (replace-by-fee)"},
    RPCResult{RPCResult::Type::BOOL, "unbroadcast", "Whether this transaction is currently unbroadcast (initial broadcast not yet acknowledged by any peers)"},
};}
static void entryToJSON(const CTxMemPool& pool, UniValue& info, const CTxMemPoolEntry& e) EXCLUSIVE_LOCKS_REQUIRED(pool.cs)
{
    AssertLockHeld(pool.cs);
    UniValue fees(UniValue::VOBJ);
    fees.pushKV("base", ValueFromAmount(e.GetFee()));
    fees.pushKV("modified", ValueFromAmount(e.GetModifiedFee()));
    fees.pushKV("ancestor", ValueFromAmount(e.GetModFeesWithAncestors()));
    fees.pushKV("descendant", ValueFromAmount(e.GetModFeesWithDescendants()));
    info.pushKV("fees", fees);
    info.pushKV("vsize", (int)e.GetTxSize());
    info.pushKV("weight", (int)e.GetTxWeight());
    info.pushKV("fee", ValueFromAmount(e.GetFee()));
    info.pushKV("modifiedfee", ValueFromAmount(e.GetModifiedFee()));
    info.pushKV("time", count_seconds(e.GetTime()));
    info.pushKV("height", (int)e.GetHeight());
    info.pushKV("descendantcount", e.GetCountWithDescendants());
    info.pushKV("descendantsize", e.GetSizeWithDescendants());
    info.pushKV("descendantfees", e.GetModFeesWithDescendants());
    info.pushKV("ancestorcount", e.GetCountWithAncestors());
    info.pushKV("ancestorsize", e.GetSizeWithAncestors());
    info.pushKV("ancestorfees", e.GetModFeesWithAncestors());
    info.pushKV("wtxid", pool.vTxHashes[e.vTxHashesIdx].first.ToString());
    const CTransaction& tx = e.GetTx();
    std::set<std::string> setDepends;