fix warnings on windows (#3555)

pytorch_lightning/metrics/converters.py

@@ -26,18 +26,14 @@ import numpy as np
 import torch
 from torch.utils.data._utils.collate import np_str_obj_array_pattern
 
-from pytorch_lightning.utilities import rank_zero_warn
 from pytorch_lightning.utilities.apply_func import apply_to_collection
 
-try:
+if torch.distributed.is_available():
     from torch.distributed import ReduceOp
-except ImportError:
-
+else:
     class ReduceOp:
         SUM = None
 
-    rank_zero_warn("Unsupported `ReduceOp` for distributed computing")
-
 
 def _apply_to_inputs(func_to_apply: Callable, *dec_args, **dec_kwargs) -> Callable:
     """

pytorch_lightning/metrics/sklearns.py

@@ -19,17 +19,13 @@ import torch
 
 from pytorch_lightning import _logger as lightning_logger
 from pytorch_lightning.metrics.metric import NumpyMetric
-from pytorch_lightning.utilities import rank_zero_warn
 
-try:
+if torch.distributed.is_available():
     from torch.distributed import group
-except ImportError:
-
+else:
     class group:
         WORLD = None
 
-    rank_zero_warn("Unsupported `group` for distributed computing.")
-
 
 class SklearnMetric(NumpyMetric):
     """