fix lint

Author: vkarpov15

lib/types/map.js

@@ -1,8 +1,6 @@
 'use strict';
 
-const Mixed = require('../schema/mixed');
 const MongooseError = require('../error/mongooseError');
-const assert = require('assert');
 const clone = require('../helpers/clone');
 const deepEqual = require('../utils').deepEqual;
 const getConstructorName = require('../helpers/getConstructorName');