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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RPCResult{RPCResult::Type::NUM, "vsize", "virtual transaction size as defined in BIP 141. This is different from actual serialized size for witness transactions as witness data is discounted."},
    RPCResult{RPCResult::Type::NUM, "weight", "transaction weight as defined in BIP 141."},
    RPCResult{RPCResult::Type::STR_AMOUNT, "fee", "transaction fee in " + CURRENCY_UNIT + " (DEPRECATED)"},
    RPCResult{RPCResult::Type::STR_AMOUNT, "modifiedfee", "transaction fee with fee deltas used for mining priority (DEPRECATED)"},
    RPCResult{RPCResult::Type::NUM_TIME, "time", "local time transaction entered pool in seconds since 1 Jan 1970 GMT"},
    RPCResult{RPCResult::Type::NUM, "height", "block height when transaction entered pool"},
    RPCResult{RPCResult::Type::NUM, "descendantcount", "number of in-mempool descendant transactions (including this one)"},
    RPCResult{RPCResult::Type::NUM, "descendantsize", "virtual transaction size of in-mempool descendants (including this one)"},
    RPCResult{RPCResult::Type::STR_AMOUNT, "descendantfees", "modified fees (see above) of in-mempool descendants (including this one) (DEPRECATED)"},
    RPCResult{RPCResult::Type::NUM, "ancestorcount", "number of in-mempool ancestor transactions (including this one)"},
    RPCResult{RPCResult::Type::NUM, "ancestorsize", "virtual transaction size of in-mempool ancestors (including this one)"},
    RPCResult{RPCResult::Type::STR_AMOUNT, "ancestorfees", "modified fees (see above) of in-mempool ancestors (including this one) (DEPRECATED)"},
    RPCResult{RPCResult::Type::STR_HEX, "wtxid", "hash of serialized transaction, including witness data"},
    RPCResult{RPCResult::Type::OBJ, "fees", "",
        {
            RPCResult{RPCResult::Type::STR_AMOUNT, "base", "transaction fee in " + CURRENCY_UNIT},
            RPCResult{RPCResult::Type::STR_AMOUNT, "modified", "transaction fee with fee deltas used for mining priority in " + CURRENCY_UNIT},
            RPCResult{RPCResult::Type::STR_AMOUNT, "ancestor", "modified fees (see above) of in-mempool ancestors (including this one) in " + CURRENCY_UNIT},
            RPCResult{RPCResult::Type::STR_AMOUNT, "descendant", "modified fees (see above) of in-mempool descendants (including this one) in " + CURRENCY_UNIT},
        }},
    RPCResult{RPCResult::Type::ARR, "depends", "unconfirmed transactions used as inputs for this transaction",