fix false alarm of event memory leak

remove the unnecessary event leak check

include/nana/gui/detail/events_operation.hpp

@@ -23,7 +23,6 @@ namespace nana
 			void register_evt(event_handle);
 			void cancel(event_handle);
 			void erase(event_handle);
-			std::size_t size() const;
 		private:
 			mutable std::recursive_mutex mutex_;
 			std::unordered_set<event_handle>	register_;