Remove optional type for ord parameter in vector_norm (#57662)
Summary:
As per discussion here https://github.com/pytorch/pytorch/pull/57127#discussion_r624948215
Note that we cannot remove the optional type from the `dim` parameter because the default is to flatten the input tensor which cannot be easily captured by a value other than `None`
### BC Breaking Note
This PR changes the `ord` parameter of `torch.linalg.vector_norm` so that it no longer accepts `None` arguments. The default behavior of `2` is equivalent to the previous default of `None`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57662
Reviewed By: albanD, mruberry
Differential Revision: D28228870
Pulled By: heitorschueroff
fbshipit-source-id: 040fd8055bbe013f64d3c8409bbb4b2c87c99d13
