Stop erroneously running aten::warn (#15124)

Stop erroneously running aten::warn (#15124)

Summary:
Fixes #15119. Before this PR, we were propagating constants through
aten::warn AND running it as a part of shape analysis.
This caused aten::warn to be run regardless of if it is
supposed to be run dynamically. This PR adds an exclusion for aten::warn
in constant propagation and shape analysis, similar to that of prim::RaiseException.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15124

Differential Revision: D13432815

Pulled By: zou3519

fbshipit-source-id: 15ab533ce2accb2da3fd4e569070c7979ce61708