[Python] Drop unnecessary null termination (project-chip#33915)

The ctypes data type `c_char_p` takes care of null-terminating the byte
array provided to it. The additional null termination doesn't hurt in
practice, but it's unnecessary.

src/controller/python/chip/ChipDeviceCtrl.py

@@ -732,7 +732,7 @@ def DiscoverCommissionableNodes(self, filterType: discovery.FilterType = discove
 
  self._ChipStack.Call(
  lambda: self._dmLib.pychip_DeviceController_DiscoverCommissionableNodes(
- self.devCtrl, int(filterType), str(filter).encode("utf-8") + b"\x00")).raise_on_error()
+ self.devCtrl, int(filterType), str(filter).encode("utf-8"))).raise_on_error()
 
  if timeoutSecond != 0:
  if stopOnFirst:
@@ -2019,7 +2019,7 @@ def CommissionOnNetwork(self, nodeId: int, setupPinCode: int,
  self._enablePairingCompeleteCallback(True)
  self._ChipStack.Call(
  lambda: self._dmLib.pychip_DeviceController_OnNetworkCommission(
- self.devCtrl, self.pairingDelegate, nodeId, setupPinCode, int(filterType), str(filter).encode("utf-8") + b"\x00" if filter is not None else None, discoveryTimeoutMsec)
+ self.devCtrl, self.pairingDelegate, nodeId, setupPinCode, int(filterType), str(filter).encode("utf-8") if filter is not None else None, discoveryTimeoutMsec)
  ).raise_on_error()
 
  return self._commissioning_complete_future.result()
@@ -2032,15 +2032,13 @@ def CommissionWithCode(self, setupPayload: str, nodeid: int, discoveryType: Disc
  '''
  self.CheckIsActive()
 
- setupPayload = setupPayload.encode() + b'\0'
-
  self._commissioning_complete_future = concurrent.futures.Future()
 
  try:
  self._enablePairingCompeleteCallback(True)
  self._ChipStack.Call(
  lambda: self._dmLib.pychip_DeviceController_ConnectWithCode(
- self.devCtrl, setupPayload, nodeid, discoveryType.value)
+ self.devCtrl, setupPayload.encode("utf-8"), nodeid, discoveryType.value)
  ).raise_on_error()
 
  return self._commissioning_complete_future.result()