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.

template<typename T, typename Tk, typename... Args>
static inline bool SetHasKeys(const std::set<T>& set, const Tk& key, const Args&... args)
{
    return (set.count(key) != 0) || SetHasKeys(set, args...);
}
static constexpr size_t PER_UTXO_OVERHEAD = sizeof(COutPoint) + sizeof(uint32_t) + sizeof(bool);
static RPCHelpMan getblockstats()
{
    return RPCHelpMan{"getblockstats",
                "\nCompute per block statistics for a given window. All amounts are in satoshis.\n"
                "It won't work for some heights with pruning.\n",
                {
                    {"hash_or_height", RPCArg::Type::NUM, RPCArg::Optional::NO, "The block hash or height of the target block", "", {"", "string or numeric"}},
                    {"stats", RPCArg::Type::ARR, RPCArg::DefaultHint{"all values"}, "Values to plot (see result below)",
                        {
                            {"height", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Selected statistic"},
                            {"time", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Selected statistic"},