Fix a FIXME in test_nn (#22675)
Summary:
https://github.com/pytorch/pytorch/issues/17262 is already resolved, so this should pass now.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22675
Differential Revision: D16188003
Pulled By: zou3519
fbshipit-source-id: 32693229a0590b274ed1bf76b815f17e77c2d3ea
