Remove vis_encode_type from list of required (#3677)

Author: Ervin T

ml-agents/mlagents/trainers/sac/trainer.py

@@ -73,7 +73,6 @@ def __init__(
             "memory_size",
             "model_path",
             "reward_signals",
-            "vis_encode_type",
         ]
 
         self._check_param_keys()