Revert "[core ATen IR] Add decompositions for max, min, var_mean (#110906)"
This reverts commit 9606cda64e97210cfcca07110ef4872cedc5a1d9.
Reverted https://github.com/pytorch/pytorch/pull/110906 on behalf of https://github.com/SS-JIA due to Breaks internal CI ([comment](https://github.com/pytorch/pytorch/pull/110906#issuecomment-1757490740))
