[NFC] Fix comment.

arc.m

@@ -855,7 +855,8 @@ OBJC_PUBLIC id objc_loadWeakRetained(id* addr)
 	// will acquire the lock before attempting to deallocate)
 	if (obj == nil)
 	{
-		// If we've destroyed this weak ref, then make sure that we also deallocate the object.
+		// If the object is destroyed, drop this reference to the WeakRef
+		// struct.
 		if (ref != NULL)
 		{
 			weakRefRelease(ref);