fix env pool test bug

Author: ruoyuGao

ding/entry/__init__.py

@@ -5,7 +5,6 @@
 from .serial_entry_onpolicy import serial_pipeline_onpolicy
 from .serial_entry_onpolicy_ppg import serial_pipeline_onpolicy_ppg
 from .serial_entry_offline import serial_pipeline_offline
-from .serial_entry_ngu import serial_pipeline_ngu
 from .serial_entry_decision_transformer import serial_pipeline_dt
 from .serial_entry_reward_model_offpolicy import serial_pipeline_reward_model_offpolicy
 from .serial_entry_reward_model_onpolicy import serial_pipeline_reward_model_onpolicy