action_server: fix heap corruption on destruction

We need to make sure no callbacks are called once detructed.

src/mavsdk/plugins/action_server/action_server_impl.cpp

@@ -196,7 +196,10 @@ void ActionServerImpl::init()
         this);
 }
 
-void ActionServerImpl::deinit() {}
+void ActionServerImpl::deinit()
+{
+    _server_component_impl->unregister_all_mavlink_command_handlers(this);
+}
 
 void ActionServerImpl::enable() {}