[air] Do not warn of checkpoint_dir if it's coming from us (base_trainer).

python/ray/train/base_trainer.py

@@ -353,7 +353,7 @@ def train_func(config, checkpoint_dir=None):
         # stdout messages and the results directory.
         train_func.__name__ = trainer_cls.__name__
 
-        trainable_cls = wrap_function(train_func)
+        trainable_cls = wrap_function(train_func, warn=False)
 
         class TrainTrainable(trainable_cls):
             """Add default resources to the Trainable."""