Removing unnecessary import.

python/unitytrainers/trainer_controller.py

 from unitytrainers import Curriculum
 from unityagents import UnityEnvironment, UnityEnvironmentException
 
-from communicator_objects import UnityRLInitializationInput
-
 
 class TrainerController(object):
     def __init__(self, env_path, run_id, save_freq, curriculum_file, fast_simulation, load, train,