DebugInfo: Drop rest of DIDescriptor subclasses

Delete the remaining subclasses of (the already deleted) `DIDescriptor`.
Part of PR23080.

llvm-svn: 235404
diff --git a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
index 1e3c5d7..9cb0aab 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DbgValueHistoryCalculator.cpp
@@ -204,7 +204,7 @@
       // Use the base variable (without any DW_OP_piece expressions)
       // as index into History. The full variables including the
       // piece expressions are attached to the MI.
-      MDLocalVariable *RawVar = MI.getDebugVariable();
+      const MDLocalVariable *RawVar = MI.getDebugVariable();
       assert(RawVar->isValidLocationForIntrinsic(MI.getDebugLoc()) &&
              "Expected inlined-at fields to agree");
       InlinedVariable Var(RawVar, MI.getDebugLoc()->getInlinedAt());