Remove instances where async is required but not used

GitOrigin-RevId: a202a2d90c4ce61391aabbde1f24437caef54ff0

services/document-updater/app/js/DeleteQueueManager.js

@@ -16,7 +16,6 @@ const RedisManager = require('./RedisManager')
 const ProjectManager = require('./ProjectManager')
 const logger = require('@overleaf/logger')
 const metrics = require('./Metrics')
-const async = require('async')
 
 // Maintain a sorted set of project flushAndDelete requests, ordered by timestamp
 // (ZADD), and process them from oldest to newest. A flushAndDelete request comes