test: remove bare CTransaction .rehash()/.calc_sha256() calls

Since the previous commit, CTransaction object calls to the
methods `.rehash()` and `.calc_sha256()` are effectively no-ops
if the returned value is not used, so we can just remove them.

test/functional/feature_rbf.py

@@ -106,7 +106,6 @@ class ReplaceByFeeTest(BitcoinTestFramework):
 
         # Should fail because we haven't changed the fee
         tx.vout[0].scriptPubKey[-1] ^= 1
-        tx.rehash()
         tx_hex = tx.serialize().hex()
 
         # This will raise an exception due to insufficient fee