Op info test for `nn.functional.max_pool2d .. nn.functional.max_unpool3d`

[qihqi]

Fix the Op info test for nn.functional.max_pool2d .. nn.functional.max_unpool3d

1. Find the lines 238 to 242 of test_ops.py and remove nn.functional.max_pool2d .. nn.functional.max_unpool3d from skip_list
2. Run op_info test with pytest test/test_ops.py
3. Fix the failure.

Please refer to this guide as guide to fix:

Also refer to these PRs:

• https://github.com/pytorch/xla/pull/7343
• https://github.com/pytorch/xla/pull/7312
• https://github.com/pytorch/xla/pull/7325