remove unused import

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

     DistInstance,
 )
 from mlagents.trainers.settings import NetworkSettings
-from mlagents.trainers.torch.utils import ModelUtils, AgentAction
+from mlagents.trainers.torch.utils import ModelUtils
 from mlagents.trainers.torch.decoders import ValueHeads
 from mlagents.trainers.torch.layers import LSTM, LinearEncoder
 from mlagents.trainers.torch.model_serialization import exporting_to_onnx