Remove lambda expression being used in grpc C++ library
diff --git a/src/cpp/server/thread_pool.h b/src/cpp/server/thread_pool.h
index 6225d82..41e2009 100644
--- a/src/cpp/server/thread_pool.h
+++ b/src/cpp/server/thread_pool.h
@@ -58,6 +58,8 @@
   bool shutdown_;
   std::queue<std::function<void()>> callbacks_;
   std::vector<std::thread> threads_;
+
+  void ThreadFunc();
 };
 
 }  // namespace grpc