Remove unused require

src/apphealthmonitor.js

@@ -5,7 +5,6 @@ var appdb = require('./appdb.js'),
     assert = require('assert'),
     async = require('async'),
     DatabaseError = require('./databaseerror.js'),
-    config = require('./config.js'),
     debug = require('debug')('box:apphealthmonitor'),
     docker = require('./docker.js').connection,
     mailer = require('./mailer.js'),