doc: correct MiniMiner constructor comment #35711

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The constructor comment refers to MiniMinerMempoolEntrys, which is not an existing type or member.

The implementation stores the relevant mempool transaction data in m_entries_by_txid, so update the comment to name the actual destination.

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35711.

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Thank you for your contribution, but I think this is correct as is and doesn't need changing: MiniMinerMempoolEntry is the underlying type in m_entries_by_txid. Closing this again.