Revert "[inductor] Optimize welford reduction (#120330)"
This reverts commit 7eb7ac815f0247a62b621897cea95ec4ca56d52e.
Reverted https://github.com/pytorch/pytorch/pull/120330 on behalf of https://github.com/kit1980 due to Broke internal tests, see D54230858 ([comment](https://github.com/pytorch/pytorch/pull/120330#issuecomment-1971878323))
