Remove more feature in product mode

runtime/vm/thread_interrupter.cc

Index: runtime/vm/thread_interrupter.cc
diff --git a/runtime/vm/thread_interrupter.cc b/runtime/vm/thread_interrupter.cc
index 920baf6b564cc653138ba9a17cbbd0deeb795a15..e11770387d77cf06a3a959839f6185cfe49e073b 100644
--- a/runtime/vm/thread_interrupter.cc
+++ b/runtime/vm/thread_interrupter.cc
@@ -11,6 +11,8 @@
 
 namespace dart {
 
+#ifndef PRODUCT
+
 // Notes:
 //
 // The ThreadInterrupter interrupts all threads actively running isolates once
@@ -224,4 +226,6 @@ void ThreadInterrupter::ThreadMain(uword parameters) {
   }
 }
 
+#endif  // !PRODUCT
+
 }  // namespace dart