clean up dataclasses installation to only <3.7 (#46182)
Summary:
clean up docker image installation of dataclasses.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46182
Reviewed By: glaringlee
Differential Revision: D24257553
Pulled By: walterddr
fbshipit-source-id: 065a607f52c7e1dc6d0765d87e4468d1752c063b
