[RegionInfo] Some cleanups

- Use unique_ptr instead of managing a container of new'd pointers.
- Use range based for loops.

No functional change is intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276001 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed