swift234

Revert "[sil-simplify-cfg] Generalize simplifySwitchEnumToSelectEnum to simplify arbitrary simple switch_enum diamonds into select_enums."

SimplifyCFG is not maintaining the dom/postdom tree. This code assumes it is and
so is using an potentially invalid domtree.

This caused SIL verifier errors compiling the perf test suite on my machine:

"SIL verification failed: instruction isn't dominated by its operand: Dominance->properlyDominates(valueI, I)
Verifying instruction:
...
->   %639 = select_enum %634 : $Optional<Int -> ()>, default %731 : $Builtin.Word
In function @_TF11DriverUtils14findTestsToRunFT_T_ basic block:"

This reverts commit r22843.

Swift SVN r22850