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

lib/CodeGen/AsmPrinter/DwarfFile.h

@@ -28,7 +28,6 @@ class DwarfUnit;
 class DIEAbbrev;
 class MCSymbol;
 class DIE;
-class DISubprogram;
 class LexicalScope;
 class StringRef;
 class DwarfDebug;