[LCG] Remove two unused typedefs from the iterators.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207052 91177308-0d34-0410-b5e6-96231b3b80d8
[LCG] Normalize the post-order SCC iterator to just iterate over the SCC
values rather than having pointers in weird places.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207053 91177308-0d34-0410-b5e6-96231b3b80d8