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_assumevalid.py

@@ -119,7 +119,6 @@ class AssumeValidTest(BitcoinTestFramework):
         tx = CTransaction()
         tx.vin.append(CTxIn(COutPoint(self.block1.vtx[0].sha256, 0), scriptSig=b""))
         tx.vout.append(CTxOut(49 * 100000000, CScript([OP_TRUE])))
-        tx.calc_sha256()
 
         block102 = create_block(self.tip, create_coinbase(height), self.block_time, txlist=[tx])
         self.block_time += 1