Optimize backward for torch.repeat (#46726)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46726
Fixes #43192
Test Plan: Imported from OSS
Reviewed By: albanD
Differential Revision: D24481801
Pulled By: ejguan
fbshipit-source-id: 95c155e0de83b71f173c9135732ea84ba6399d69
