remove unused require

src/user.js

@@ -36,7 +36,6 @@ var assert = require('assert'),
     groups = require('./groups.js'),
     GroupError = groups.GroupError,
     hat = require('hat'),
-    mail = require('./mail.js'),
     mailer = require('./mailer.js'),
     mailboxdb = require('./mailboxdb.js'),
     safe = require('safetydance'),