fix jest

packages/hydrooj/src/service/db.ts

@@ -1,5 +1,4 @@
 import mongodb from 'mongodb';
-import MongoWatcher from 'mongodb-watcher';
 import * as bus from './bus';
 import options from '../options';
 
@@ -16,12 +15,6 @@ mongodb.MongoClient.connect(mongourl, { useNewUrlParser: true, useUnifiedTopolog
     .then((Client) => {
         db = Client.db(opts.name);
         global.Hydro.service.db.db = db;
-        // eslint-disable-next-line @typescript-eslint/no-unused-vars
-        const watcher = new MongoWatcher(db, {
-            longCursorThreshold: 100,
-            largeInsertThreshold: 1024 * 30,
-            largeFetchThreshold: 1024 * 30,
-        });
         bus.publish('system_database_connected', null);
     });