Revert "[dtensor] switch mean to use reduction linear (#97996)"
This reverts commit 1b323b313ce35c03583ece017f928079f4a86882.
Reverted https://github.com/pytorch/pytorch/pull/97996 on behalf of https://github.com/huydhn due to Sorry for reverting your PR, but it fails a test on CPU https://hud.pytorch.org/pytorch/pytorch/commit/1b323b313ce35c03583ece017f928079f4a86882
