Fix the error in the note about `torch.device` documentation. (#16839)

Fix the error in the note about `torch.device` documentation. (#16839)

Summary:
This PR is a simple fix for the mistake in the first note for `torch.device` in the "tensor attributes" doc.
![image](https://user-images.githubusercontent.com/8536399/52399611-1becaa00-2b00-11e9-85bf-cac04b29842d.png)

```
>>> # You can substitute the torch.device with a string
>>> torch.randn((2,3), 'cuda:1')
```
Above code will cause error like below:
```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-53-abdfafb67ab1> in <module>()
----> 1 torch.randn((2,3), 'cuda:1')

TypeError: randn() received an invalid combination of arguments - got (tuple, str), but expected one of:
 * (tuple of ints size, torch.Generator generator, Tensor out, torch.dtype dtype, torch.layout layout, torch.device device, bool requires_grad)
 * (tuple of ints size, Tensor out, torch.dtype dtype, torch.layout layout, torch.device device, bool requires_grad)
```

Simply adding the argument name `device` solves the problem: `torch.randn((2,3), device='cuda:1')`.

However, another concern is that this note seems redundant as **there is already another note covering this usage**:
![image](https://user-images.githubusercontent.com/8536399/52399583-0ecfbb00-2b00-11e9-914f-e95da4edecd1.png)

So maybe it's better to just remove this note?
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16839

Reviewed By: ezyang

Differential Revision: D13989209

Pulled By: gchanan

fbshipit-source-id: ac255d52528da053ebfed18125ee6b857865ccaf