DebugInfo: Gut DIObjCProperty and DIImportedEntity

Gut a couple more classes in the DIDescriptor hierarchy.  Leave behind
an implicit conversion to `DIDescriptor`, the old base class.

llvm-svn: 234836
diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index 2c3d00b..fe74ec5 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -163,7 +163,7 @@
       for (auto *RT : CU->getRetainedTypes())
         processType(RT);
       for (DIImportedEntity Import : CU->getImportedEntities()) {
-        DIDescriptor Entity = Import.getEntity().resolve(TypeIdentifierMap);
+        auto *Entity = Import->getEntity().resolve(TypeIdentifierMap);
         if (auto *T = dyn_cast<MDType>(Entity))
           processType(T);
         else if (auto *SP = dyn_cast<MDSubprogram>(Entity))