Remove some Python 2 compatibility code. (#6624)

python/ray/tune/tests/test_checkpoint_manager.py

@@ -6,14 +6,10 @@ from __future__ import print_function
 import random
 import sys
 import unittest
+from unittest.mock import patch
 
 from ray.tune.checkpoint_manager import Checkpoint, CheckpointManager, logger
 
-if sys.version_info >= (3, 3):
-    from unittest.mock import patch
-else:
-    from mock import patch
-
 
 class CheckpointManagerTest(unittest.TestCase):
     @staticmethod
@@ -108,5 +104,4 @@ class CheckpointManagerTest(unittest.TestCase):
 
 if __name__ == "__main__":
     import pytest
-    import sys
     sys.exit(pytest.main(["-v", __file__]))