[torch/distributed] Fix pydoc for torch.distributed.elastic.multiprocessing (replace Redirect with Std)
Summary: `Redirects` was renamed to `Std` in `torch.distributed.elastic.multiprocessing.api`. Pointed out by a user in https://github.com/pytorch/elastic/issues/147.
Test Plan: N/A just doc change
Reviewed By: tierex
Differential Revision: D27866614
fbshipit-source-id: 9fb901aae7ebe11cde13000a1c118de527f34400
