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.

{
        ChainstateManager& chainman = EnsureAnyChainman(request.context);
        LOCK(cs_main);
        pblockindex = chainman.m_blockman.LookupBlockIndex(hash);
        tip = chainman.ActiveChain().Tip();
        if (!pblockindex) {
            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
        }
        block = GetBlockChecked(pblockindex);
    }
    if (verbosity <= 0)
    {
        CDataStream ssBlock(SER_NETWORK, PROTOCOL_VERSION | RPCSerializationFlags());
        ssBlock << block;
        std::string strHex = HexStr(ssBlock);
        return strHex;
    }
    TxVerbosity tx_verbosity;
    if (verbosity == 1) {
        tx_verbosity = TxVerbosity::SHOW_TXID;
    } else if (verbosity == 2) {
        tx_verbosity = TxVerbosity::SHOW_DETAILS;
    } else {
        tx_verbosity = TxVerbosity::SHOW_DETAILS_AND_PREVOUT;
    }
    return blockToJSON(block, tip, pblockindex, tx_verbosity);
},
    };
}
static RPCHelpMan pruneblockchain()