Remove WFTaskFactory::release_guard() with default NULL message.

src/factory/WFTaskFactory.h

@@ -306,21 +306,10 @@ class WFTaskFactory
 	/* The 'guard' is acquired after started, so call 'release_guard' after
 	   and only after the task is finished, typically in its callback.
 	   The function returns 1 if another is signaled, otherwise returns 0. */
-	static int release_guard(const std::string& resource_name)
-	{
-		return WFTaskFactory::release_guard(resource_name, NULL);
-	}
-
 	static int release_guard(const std::string& resaource_name, void *msg);
 
-	static int release_guard_safe(const std::string& resource_name)
-	{
-		return WFTaskFactory::release_guard_safe(resource_name, NULL);
-	}
-
 	static int release_guard_safe(const std::string& resource_name, void *msg);
 
-
 public:
 	template<class FUNC, class... ARGS>
 	static WFGoTask *create_go_task(const std::string& queue_name,