Correct documentation for torch.unsqueeze (#33478)
Summary:
"out" argument in torch.unsqueeze is not actually implemented, fixed documentation https://github.com/pytorch/pytorch/issues/29800
After: 
Before: 
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33478
Differential Revision: D19978477
Pulled By: yf225
fbshipit-source-id: 42337326c1ec04975307366c94591ee32a11b091
