test: rename CTransaction .rehash()/.hash -> .txid_hex for consistency

Note that we unfortunately can't use a scripted diff here, as the same
property and method name is also used for `CBlockHeader`/`CBlock` instances.

test/functional/interface_usdt_mempool.py

@@ -323,7 +323,7 @@ class MempoolTracepointTest(BitcoinTestFramework):
         self.log.info("Ensuring mempool:rejected event was handled successfully...")
         assert_equal(1, len(events))
         event = events[0]
-        assert_equal(bytes(event.hash)[::-1].hex(), tx["tx"].hash)
+        assert_equal(bytes(event.hash)[::-1].hex(), tx["tx"].txid_hex)
         assert_equal(event.reason.decode("UTF-8"), "min relay fee not met")
 
         bpf.cleanup()