engine: remove unused FLB_ENGINE_STATS event mask
#define FLB_ENGINE_EV_FAILED FLB_BITS_U64_SET(1, 2) /* Engine started */
#define FLB_ENGINE_EV_STOP FLB_BITS_U64_SET(1, 3) /* Requested to stop */
#define FLB_ENGINE_EV_SHUTDOWN FLB_BITS_U64_SET(1, 4) /* Engine shutdown */
-#define FLB_ENGINE_EV_STATS FLB_BITS_U64_SET(1, 5) /* Collect stats */
/* Similar to engine events, but used as return values */
#define FLB_ENGINE_STARTED FLB_BITS_U64_LOW(FLB_ENGINE_EV_STARTED)
#define FLB_ENGINE_FAILED FLB_BITS_U64_LOW(FLB_ENGINE_EV_FAILED)
#define FLB_ENGINE_STOP FLB_BITS_U64_LOW(FLB_ENGINE_EV_STOP)
#define FLB_ENGINE_SHUTDOWN FLB_BITS_U64_LOW(FLB_ENGINE_EV_SHUTDOWN)
-#define FLB_ENGINE_STATS FLB_BITS_U64_LOW(FLB_ENGINE_EV_STATS)
/* Engine signals: Task, it only refer to the type */
#define FLB_ENGINE_TASK 2
