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.

contrib/signet/miner

@@ -40,7 +40,6 @@ def signet_txs(block, challenge):
     txs[0].vout[-1].scriptPubKey += CScriptOp.encode_op_pushdata(SIGNET_HEADER)
     hashes = []
     for tx in txs:
-        tx.rehash()
         hashes.append(ser_uint256(tx.sha256))
     mroot = block.get_merkle_root(hashes)
 
@@ -55,7 +54,6 @@ def signet_txs(block, challenge):
     to_spend.nLockTime = 0
     to_spend.vin = [CTxIn(COutPoint(0, 0xFFFFFFFF), b"\x00" + CScriptOp.encode_op_pushdata(sd), 0)]
     to_spend.vout = [CTxOut(0, challenge)]
-    to_spend.rehash()
 
     spend = CTransaction()
     spend.version = 0
@@ -88,7 +86,6 @@ def finish_block(block, signet_solution, grind_cmd):
         pass # Don't need to add a signet commitment if there's no signet signature needed
     else:
         block.vtx[0].vout[-1].scriptPubKey += CScriptOp.encode_op_pushdata(SIGNET_HEADER + signet_solution)
-        block.vtx[0].rehash()
         block.hashMerkleRoot = block.calc_merkle_root()
     if grind_cmd is None:
         block.solve()
@@ -111,7 +108,6 @@ def new_block(tmpl, reward_spk, *, blocktime=None, poolid=None):
     cbtx.vin = [CTxIn(COutPoint(0, 0xffffffff), scriptSig, MAX_SEQUENCE_NONFINAL)]
     cbtx.vout = [CTxOut(tmpl["coinbasevalue"], reward_spk)]
     cbtx.vin[0].nSequence = 2**32-2
-    cbtx.rehash()
 
     block = CBlock()
     block.nVersion = tmpl["version"]
@@ -130,7 +126,6 @@ def new_block(tmpl, reward_spk, *, blocktime=None, poolid=None):
     block.vtx[0].wit.vtxinwit = [cbwit]
     block.vtx[0].vout.append(CTxOut(0, bytes(get_witness_script(witroot, witnonce))))
 
-    block.vtx[0].rehash()
     block.hashMerkleRoot = block.calc_merkle_root()
 
     return block