Hardware specific parts of Accelerator Refactoring

docs/source/common/trainer.rst

@@ -1121,7 +1121,7 @@ To define your own behavior, subclass the relevant class and pass it in. Here's
 
 .. code-block:: python
 
-    from pytorch_lightning.cluster_environments import cluster_environment
+    from pytorch_lightning.environments import cluster_environment
 
     class MyCluster(ClusterEnvironment):
 

docs/source/extensions/accelerators.rst

@@ -70,7 +70,7 @@ First, implement your own ClusterEnvironment. Here is the torch elastic implemen
     import os
     from pytorch_lightning import _logger as log
     from pytorch_lightning.utilities import rank_zero_warn
-    from pytorch_lightning.cluster_environments.cluster_environment import ClusterEnvironment
+    from pytorch_lightning.environments.cluster_environment import ClusterEnvironment
 
     class TorchElasticEnvironment(ClusterEnvironment):
 

pytorch_lightning/accelerators/accelerator.py

@@ -347,8 +347,7 @@ def amp_backend(self) -> Optional[LightningEnum]:
             return AMPType.APEX
         elif isinstance(self.precision_plugin, NativeMixedPrecisionPlugin):
             return AMPType.NATIVE
-        else:
-            return None
+        return None
 
     @property
     def precision(self) -> int: