fix simple test env

ml-agents/mlagents/trainers/tests/simple_test_envs.py

     DecisionSteps,
     TerminalSteps,
     BehaviorMapping,
-    BehaviorName,
-    ActionBuffer,
 )
 from mlagents_envs.tests.test_rpc_utils import proto_from_steps_and_action
 from mlagents_envs.communicator_objects.agent_info_action_pair_pb2 import (