DebugInfo: Gut DISubprogram and DILexicalBlock*

Gut the `DIDescriptor` wrappers around `MDLocalScope` subclasses.  Note
that `DILexicalBlock` wraps `MDLexicalBlockBase`, not `MDLexicalBlock`.

llvm-svn: 234850
diff --git a/llvm/lib/CodeGen/LexicalScopes.cpp b/llvm/lib/CodeGen/LexicalScopes.cpp
index 938fa0a..d6998d6 100644
--- a/llvm/lib/CodeGen/LexicalScopes.cpp
+++ b/llvm/lib/CodeGen/LexicalScopes.cpp
@@ -157,8 +157,7 @@
                                                     false)).first;
 
   if (!Parent) {
-    assert(
-        DISubprogram(cast<MDSubprogram>(Scope)).describes(MF->getFunction()));
+    assert(cast<MDSubprogram>(Scope)->describes(MF->getFunction()));
     assert(!CurrentFnLexicalScope);
     CurrentFnLexicalScope = &I->second;
   }