Remove pathlib install command as it is built-in 3.8. (#613)
Summary:
pathlib is built-in in py38, so we don't need to install it in CI.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/613
Test Plan: V1 CI (https://github.com/pytorch/benchmark/actions/runs/1545941996)
Reviewed By: erichan1
Differential Revision: D32893267
Pulled By: xuzhao9
fbshipit-source-id: 85fe366ca43ec44d4cdc97eaf6b24d6f5a5c6ed0
