delete unnecessary file

packages/app/src/server/events/activity.ts

@@ -1,20 +0,0 @@
-import { EventEmitter } from 'events';
-import loggerFactory from '../../utils/logger';
-
-const logger = loggerFactory('growi:events:activity');
-
-
-class ActivityEvent extends EventEmitter {
-
-  onRemove(action: string, activity: any): void {
-    logger.info('onRemove activity event fired');
-  }
-
-  onCreate(action: string, activity: any): void {
-    logger.info('onCreate activity event fired');
-  }
-
-}
-
-const instance = new ActivityEvent();
-export default instance;