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/feature_assumeutxo.py

@@ -605,7 +605,7 @@ class AssumeutxoTest(BitcoinTestFramework):
         privkey = n0.get_deterministic_priv_key().key
         raw_tx = n1.createrawtransaction([prevout], {getnewdestination()[2]: 24.99})
         signed_tx = n1.signrawtransactionwithkey(raw_tx, [privkey], [prevout])['hex']
-        signed_txid = tx_from_hex(signed_tx).rehash()
+        signed_txid = tx_from_hex(signed_tx).txid_hex
 
         assert n1.gettxout(prev_tx['txid'], 0) is not None
         n1.sendrawtransaction(signed_tx)