Revert r290512: [ADT] Add a generic concatenating iterator and range.

This code doesn't work on MSVC for reasons that elude me and I've not
yet covinced a workaround to compile cleanly so reverting for now while
I play with it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290513 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed