test: avoid unneeded (w)txid hex -> integer conversions

Rather than determining a CTransaction's (w)txid as an integer by
converting it's hex value, it can be directly accessed via the
introduced `.{w,}txid_int` property.

test/functional/feature_utxo_set_hash.py

@@ -55,7 +55,7 @@ class UTXOSetHashTest(BitcoinTestFramework):
                     if (coinbase and n > 0):
                         continue
 
-                    data = COutPoint(int(tx.txid_hex, 16), n).serialize()
+                    data = COutPoint(tx.txid_int, n).serialize()
                     data += (height * 2 + coinbase).to_bytes(4, "little")
                     data += tx_out.serialize()