Revert r361811: 'Re-commit r357452 (take 2): "SimplifyCFG SinkCommonCodeFromPredecess...

Revert r361811: 'Re-commit r357452 (take 2): "SimplifyCFG SinkCommonCodeFromPredecessors ...'

We have observed some failures with internal builds with this revision.

- Performance regressions:
  - llvm's SingleSource/Misc evalloop shows performance regressions (although these may be red herrings).
  - Benchmarks for Abseil's SwissTable.
- Correctness:
  - Failures for particular libicu tests when building the Google AppEngine SDK (for PHP).

hwennborg has already been notified, and is aware of reproducer failures.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@363220 91177308-0d34-0410-b5e6-96231b3b80d8