swift234

Revert "Fix post-dominator tree in stack promotion"

This broke the test suite under optimizations with a SIL verifier error: "stack dealloc does
not match most recent stack alloc".

This reverts commit 7a2ca23bc27d932ab30fe22d4e635048ddd0bcf8, reversing
changes made to 4c55e8d7a7973657e2fb510aaf13f3c3c8c9a80e.