Cleanup: Replace a redundant statement with an assertion

storage/innobase/sync/sync0debug.cc

@@ -1580,7 +1580,7 @@ struct CreateTracker {
 	~CreateTracker()
 		UNIV_NOTHROW
 	{
-		ut_d(m_files.empty());
+		ut_ad(m_files.empty());
 
 		m_mutex.destroy();
 	}