Remove free() in mo_task_cancel()

This commit removes redundant free() in mo_task_cancel() which
has been called in list_remove().

Author: vicLin8712

kernel/task.c

@@ -670,7 +670,6 @@ int32_t mo_task_cancel(uint16_t id)
     /* Free memory outside critical section */
     free(tcb->stack);
     free(tcb);
-    free(node);
     return ERR_OK;
 }