[LoopSimplifyCFG] Add missing MSSA edge deletion

When we create fictive switch in preheader, we should take
care about MSSA and delete edge between old preheader and
header.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354547 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed