Remove (object) from class declarations. (#6658)

python/ray/tune/trainable.py

@@ -29,7 +29,7 @@ logger = logging.getLogger(__name__)
 SETUP_TIME_THRESHOLD = 10
 
 
-class Trainable(object):
+class Trainable:
     """Abstract class for trainable models, functions, etc.
 
     A call to ``train()`` on a trainable will execute one logical iteration of