message: test: Hide tx rehash in helper
  This avoids code-bloat and accidentally forgetting to call it
diff: @@ -51,6 +51,7 @@ def cltv_modify_tx(node, tx, prepend_scriptsig, nsequence=None, nlocktime=None):
  tx.deserialize(BytesIO(hex_str_to_bytes(signed_result['hex'])))
  tx.vin[0].scriptSig = CScript(prepend_scriptsig + list(CScript(tx.vin[0].scriptSig)))
  + tx.rehash()
  return tx
  @@ -124,7 +125,6 @@ class BIP65Test(BitcoinTestFramework):
  spendtx = create_transaction(self.nodes[0], self.coinbase_txids[i],
  self.nodeaddress, amount=1.0)
  spendtx = cltv_invalidate(self.nodes[0], spendtx, i)
  - spendtx.rehash()
  invalid_ctlv_txs.append(spendtx)
  tip = self.nodes[0].getbestblockhash()
  @@ -161,7 +161,6 @@ class BIP65Test(BitcoinTestFramework):
  spendtx = create_transaction(self.nodes[0], self.coinbase_txids[10+i],
  self.nodeaddress, amount=1.0)
  spendtx = cltv_invalidate(self.nodes[0], spendtx, i)
  - spendtx.rehash()
  expected_cltv_reject_reason = [
  "non-mandatory-script-verify-flag (Operation not valid with the current stack size)",
  @@ -195,7 +194,6 @@ class BIP65Test(BitcoinTestFramework):
  self.log.info("Test that a version 4 block with a valid-according-to-CLTV transaction is accepted")
  spendtx = cltv_validate(self.nodes[0], spendtx, CLTV_HEIGHT - 1)
  - spendtx.rehash()
  block.vtx.pop(1)
  block.vtx.append(spendtx)
  