Revert "[IRSim][IROutliner] Add support for outlining PHINodes with the rest of the region."

This reverts commit 515eec3553b02533e9a88ee84bc245d5415163da.

By mistake, commit message was not complete.

GitOrigin-RevId: e50b217b4e6fb0be9b93d760e01462c117fe9318
14 files changed