Revert "[inductor] Optimize welford reduction (#120330)"
This reverts commit 4c6ba16f825ca7b99133efca95da0b7112add66b.
Reverted https://github.com/pytorch/pytorch/pull/120330 on behalf of https://github.com/jeffdaily due to broke ROCm CI while ROCm was in unstable status ([comment](https://github.com/pytorch/pytorch/pull/120330#issuecomment-1961623739))
