fix guard_fn issue (#3815)

Author: lanluo-nvidia

tests/py/dynamo/conversion/harness.py

@@ -26,11 +26,17 @@
     post_lowering,
     pre_export_lowering,
 )
+from torch_tensorrt.dynamo.lowering.passes import remove_num_users_is_0_nodes
 from torch_tensorrt.dynamo.runtime import PythonTorchTensorRTModule
 from torch_tensorrt.dynamo.utils import ATOL, RTOL, get_model_device, get_torch_inputs
 
 _LOGGER: logging.Logger = logging.getLogger(__name__)
 
+# this is the post lowering pass list for the converter test
+post_lowering_pass_list_for_converter_test = [
+    remove_num_users_is_0_nodes,
+]
+
 
 # this method is only used in our converter test to infer the module output dtypes via dummy inference
 # which is due to fx.symbolic_trace does not have the meta['val'] info in the node
@@ -435,6 +441,8 @@ def run_test(
             settings=compilation_settings,
         )
 
+        for pass_func in post_lowering_pass_list_for_converter_test:
+            mod = pass_func(mod, compilation_settings)
         num_inputs = len(inputs)
         trt_inputs = inputs
         dtype_to_change = []