Replace mismatched delete with swift_cxx_deleteObject

The `allocatedEntry` is allocated with `swift_cxx_newObject` so it
should be deallocated with the `swift_cxx_deleteObject`.

Author: etcwilde

stdlib/public/runtime/Metadata.cpp

@@ -1061,7 +1061,7 @@ namespace {
 
         // Otherwise, use the new entry and destroy the one we allocated.
         assert(existingEntry && "spurious failure of strong compare-exchange?");
-        delete allocatedEntry;
+        swift_cxx_deleteObject(allocatedEntry);
       }
 
       return { static_cast<SingletonMetadataCacheEntry*>(existingEntry), false };