DebugInfo: Delete subclasses of DIScope

Delete subclasses of (the already defunct) `DIScope`, updating users to
use the raw pointers from the `Metadata` hierarchy directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235356 91177308-0d34-0410-b5e6-96231b3b80d8
19 files changed