message: test: feature_cltv.py: don't return tx copies in modification functions
  The functions cltv_modify_tx(), cltv_invalidate() and cltv_validate()
  all modify the passed transaction in-place, i.e. there is no need
  to return a copy.
diff: @@ -45,7 +45,6 @@ def cltv_modify_tx(tx, prepend_scriptsig, nsequence=None, nlocktime=None):
  tx.vin[0].scriptSig = CScript(prepend_scriptsig + list(CScript(tx.vin[0].scriptSig)))
  tx.rehash()
  - return tx
  def cltv_invalidate(tx, failure_reason):
  @@ -69,14 +68,14 @@ def cltv_invalidate(tx, failure_reason):
  [[CScriptNum(500), OP_CHECKLOCKTIMEVERIFY, OP_DROP], 0xffffffff, 500],
  ][failure_reason]
  - return cltv_modify_tx(tx, prepend_scriptsig=scheme[0], nsequence=scheme[1], nlocktime=scheme[2])
  + cltv_modify_tx(tx, prepend_scriptsig=scheme[0], nsequence=scheme[1], nlocktime=scheme[2])
  def cltv_validate(tx, height):
  # Modify the signature in vin 0 and nSequence/nLockTime of the tx to pass CLTV
  scheme = [[CScriptNum(height), OP_CHECKLOCKTIMEVERIFY, OP_DROP], 0, height]
  - return cltv_modify_tx(tx, prepend_scriptsig=scheme[0], nsequence=scheme[1], nlocktime=scheme[2])
  + cltv_modify_tx(tx, prepend_scriptsig=scheme[0], nsequence=scheme[1], nlocktime=scheme[2])
  class BIP65Test(BitcoinTestFramework):
  @@ -114,7 +113,7 @@ class BIP65Test(BitcoinTestFramework):
  invalid_cltv_txs = []
  for i in range(5):
  spendtx = wallet.create_self_transfer(from_node=self.nodes[0])['tx']
  - spendtx = cltv_invalidate(spendtx, i)
  + cltv_invalidate(spendtx, i)
  invalid_cltv_txs.append(spendtx)
  tip = self.nodes[0].getbestblockhash()
  @@ -149,7 +148,7 @@ class BIP65Test(BitcoinTestFramework):
  # create and test one invalid tx per CLTV failure reason (5 in total)
  for i in range(5):
  spendtx = wallet.create_self_transfer(from_node=self.nodes[0])['tx']
  - spendtx = cltv_invalidate(spendtx, i)
  + cltv_invalidate(spendtx, i)
  expected_cltv_reject_reason = [
  "non-mandatory-script-verify-flag (Operation not valid with the current stack size)",
  @@ -182,7 +181,7 @@ class BIP65Test(BitcoinTestFramework):
  peer.sync_with_ping()
  self.log.info("Test that a version 4 block with a valid-according-to-CLTV transaction is accepted")
  - spendtx = cltv_validate(spendtx, CLTV_HEIGHT - 1)
  + cltv_validate(spendtx, CLTV_HEIGHT - 1)
  block.vtx.pop(1)
  block.vtx.append(spendtx)
  