Remove TODO and unnecessary branch/store in optimized builds.

PiperOrigin-RevId: 546382890

src/google/protobuf/metadata_lite.h

@@ -182,11 +182,11 @@ class PROTOBUF_EXPORT InternalMetadata {
 
   template <typename T>
   PROTOBUF_NOINLINE void DeleteOutOfLineHelper() {
-    // TODO(b/188560391): Determine if this branch is needed.
-    if (!arena()) {
+    ABSL_DCHECK(!arena());
     delete PtrValue<Container<T>>();
+#ifndef NDEBUG
     ptr_ = 0;
-    }
+#endif  // NDEBUG
   }
 
   template <typename T>