test: simplify (w)txid checks by avoiding .calc_sha256 calls

Calls on the tx.calc_sha256 method can be confusing, as they return
the result (either txid or wtxid, depending on the with_witness
boolean parameter) as integer rather than as actual (w)txid. Use
.rehash() and .getwtxid() instead to improve readability and in some
cases avoid a conversion from string-txid to an integer.

test/functional/feature_segwit.py

@@ -267,7 +267,7 @@ class SegWitTest(BitcoinTestFramework):
         tx1 = tx_from_hex(tx1_hex)
 
         # Check that wtxid is properly reported in mempool entry (txid1)
-        assert_equal(int(self.nodes[0].getmempoolentry(txid1)["wtxid"], 16), tx1.calc_sha256(True))
+        assert_equal(self.nodes[0].getmempoolentry(txid1)["wtxid"], tx1.getwtxid())
 
         # Check that weight and vsize are properly reported in mempool entry (txid1)
         assert_equal(self.nodes[0].getmempoolentry(txid1)["vsize"], tx1.get_vsize())
@@ -283,7 +283,7 @@ class SegWitTest(BitcoinTestFramework):
         assert not tx.wit.is_null()
 
         # Check that wtxid is properly reported in mempool entry (txid2)
-        assert_equal(int(self.nodes[0].getmempoolentry(txid2)["wtxid"], 16), tx.calc_sha256(True))
+        assert_equal(self.nodes[0].getmempoolentry(txid2)["wtxid"], tx.getwtxid())
 
         # Check that weight and vsize are properly reported in mempool entry (txid2)
         assert_equal(self.nodes[0].getmempoolentry(txid2)["vsize"], tx.get_vsize())
@@ -306,7 +306,7 @@ class SegWitTest(BitcoinTestFramework):
         assert txid3 in template_txids
 
         # Check that wtxid is properly reported in mempool entry (txid3)
-        assert_equal(int(self.nodes[0].getmempoolentry(txid3)["wtxid"], 16), tx.calc_sha256(True))
+        assert_equal(self.nodes[0].getmempoolentry(txid3)["wtxid"], tx.getwtxid())
 
         # Check that weight and vsize are properly reported in mempool entry (txid3)
         assert_equal(self.nodes[0].getmempoolentry(txid3)["vsize"], tx.get_vsize())