fix onnx input

ml-agents/mlagents/trainers/torch/model_serialization.py

     def __init__(self, policy):
         self.policy = policy
         dummy_vec_obs = [torch.zeros([1] + [self.policy.vec_obs_size])]
-        dummy_vis_obs = [torch.zeros([1] + self.policy.vis_obs_shape)] \
+        dummy_vis_obs = [torch.zeros([1] + list(self.policy.vis_obs_shape))] \
-        dummy_masks = [torch.ones([1] + self.policy.actor_critic.act_size)]
-        dummy_memories = [torch.zeros([1] + [self.policy.m_size])]
-        dummy_sequence_length = [torch.tensor([self.policy.sequence_length])]
+        dummy_masks = torch.ones([1] + self.policy.actor_critic.act_size)
+        dummy_memories = torch.zeros([1] + [self.policy.m_size])
-            "action_mask", "memories", "sequence_length"]
+            "action_mask", "memories"]
-             "action_mask": [0], "memories": [0], "action": [0],"action_probs": [0]}
+            "action_mask": [0], "memories": [0], "action": [0],"action_probs": [0]}
-            dummy_masks, dummy_memories, dummy_sequence_length)
+            dummy_masks, dummy_memories)
 
     def export_policy_model(self, output_filepath: str) -> None:
         """