make assert_equal an example how to partial `torch.testing.assert_close` (#58918)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58918
~Instead of a distinct `torch.testing.assert_close` and `torch.testing.assert_equal`, this makes `torch.testing.assert_equal` a special case of `torch.testing.assert_close` for `rtol=atol=0`. In this case the closeness definition `abs(actual - expected) <= atol + rtol * abs(expected)` boils down to `abs(actual - expected) <= 0`. Since `abs(x)` can never be `<0`, this is equivalent to `abs(a - b) == 0` and this again boils down to `a == b`.~
Following https://github.com/pytorch/pytorch/pull/58918#issuecomment-860642057 and some offline discussions, we opted to use `assert_equal` as an example how to `partial` it.
This makes maintaing the module a lot easier, because we don't need to keep two functions in sync.
Test Plan: Imported from OSS
Reviewed By: anjali411
Differential Revision: D29259404
Pulled By: mruberry
fbshipit-source-id: fa1a1fa93672a7ed1c5f0e4beb0dcd45b5c14fce
