remove async package

package.json

@@ -73,7 +73,6 @@
     "JSONStream": "^1.3.5",
     "archiver": "^3.1.1",
     "array.prototype.flatmap": "^1.2.2",
-    "async": "^3.0.1",
     "async-canvas-to-blob": "^1.0.3",
     "aws-sdk": "^2.88.0",
     "axios": "^0.19.0",

src/server/routes/login.js

@@ -7,7 +7,6 @@ module.exports = function(crowi, app) {
   const debug = require('debug')('growi:routes:login');
   const logger = require('@alias/logger')('growi:routes:login');
   const path = require('path');
-  const async = require('async');
   const mailer = crowi.getMailer();
   const User = crowi.model('User');
   const { configManager, appService, aclService } = crowi;