Step 5: remove _unique_dim in favor of unique_dim (#18654)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18654
ghimport-source-id: 63c84cedc3335719fca4a085fa19bdc57d2bc88a
Differential Revision: D15000635
Pulled By: VitalyFedyunin
fbshipit-source-id: 9e8594622a867a79d8e2b6be96579816aa22ae2d
