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_fee_estimation.py

@@ -61,7 +61,6 @@ def small_txpuzzle_randfee(
     tx.vout[0].nValue = int((total_in - amount - fee) * COIN)
     tx.vout.append(deepcopy(tx.vout[0]))
     tx.vout[1].nValue = int(amount * COIN)
-    tx.rehash()
     txid = tx.hash
     tx_hex = tx.serialize().hex()