replace underscore with our own

we only need like 5 simple functions

src/test/users-test.js

@@ -11,7 +11,7 @@ const BoxError = require('../boxerror.js'),
     safe = require('safetydance'),
     speakeasy = require('speakeasy'),
     users = require('../users.js'),
-    _ = require('underscore');
+    _ = require('../underscore.js');
 
 describe('User', function () {
     const { domainSetup, cleanup, admin, user, auditSource, checkMails, clearMailQueue } = common;