remove extraneous type information from torch.matrix_rank documentation (#28479)
Summary:
The types don't appear in the docstrings for other functions in the `torch` namespace so I think this was included here because of a copy/paste error.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28479
Differential Revision: D18086150
Pulled By: ezyang
fbshipit-source-id: 2481bccba6df36b12779a330f8c43d4aea68495f
