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_cltv.py

@@ -162,7 +162,7 @@ class BIP65Test(BitcoinTestFramework):
             ][i]
             # First we show that this tx is valid except for CLTV by getting it
             # rejected from the mempool for exactly that reason.
-            spendtx_txid = spendtx.hash
+            spendtx_txid = spendtx.txid_hex
             spendtx_wtxid = spendtx.getwtxid()
             assert_equal(
                 [{