coinstats: Fix hash_serialized2 calculation

The legacy serialization was vulnerable to maleation and is fixed by
adopting the same serialization procedure as was already in use for
MuHash.

This also includes necessary test fixes where the hash_serialized2 was
hardcoded as well as correction of the regtest chainparams.

Co-authored-by: Sebastian Falbesoner <sebastian.falbesoner@gmail.com>

test/functional/feature_utxo_set_hash.py

@@ -69,7 +69,7 @@ class UTXOSetHashTest(BitcoinTestFramework):
         assert_equal(finalized[::-1].hex(), node_muhash)
 
         self.log.info("Test deterministic UTXO set hash results")
-        assert_equal(node.gettxoutsetinfo()['hash_serialized_2'], "f9aa4fb5ffd10489b9a6994e70ccf1de8a8bfa2d5f201d9857332e9954b0855d")
+        assert_equal(node.gettxoutsetinfo()['hash_serialized_2'], "d1c7fec1c0623f6793839878cbe2a531eb968b50b27edd6e2a57077a5aed6094")
         assert_equal(node.gettxoutsetinfo("muhash")['muhash'], "d1725b2fe3ef43e55aa4907480aea98d406fc9e0bf8f60169e2305f1fbf5961b")
 
     def run_test(self):