[BE] Remove dependency on `six` and `future` (#94709)

Remove the Python 2 and 3 compatibility library [six](https://pypi.org/project/six) and [future](https://pypi.org/project/future) and `torch._six`. We only support Python 3.8+ now. It's time to retire them.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/94709
Approved by: https://github.com/malfet, https://github.com/Skylion007
diff --git a/test/test_mps.py b/test/test_mps.py
index c03e4e3..f45601fa 100644
--- a/test/test_mps.py
+++ b/test/test_mps.py
@@ -17,7 +17,7 @@
 import torch.nn.functional as F
 import itertools
 from collections import defaultdict
-from torch._six import inf
+from torch import inf
 from torch.nn import Parameter
 from torch.testing._internal import opinfo
 from torch.testing._internal.common_utils import \