Fix NewTemplate.merkle_path in bitcoind

[Fi3]

NewTemplate.merkle_path should be the smaller path possible needed to calculate the merkle root given the coinbase tx. Right now is composed by all the tx ids of the txs that are in the candidate block.

priority 6/10

[pavlenex]

@Fi3 I think we fixed this one?

[Sjors]

I think that's why the helper function GetMerklePathForCoinbase(const CBlock& block) was added to bitcoin/bitcoin#28983

If that's correct then this issue can be closed. It needs some refactoring, but that doesn't have to be tracked here.

[Fi3]

yep is correct.