Fix a perf issue caused by cloning schemaObj (#101)

Co-authored-by: Ray Chen <raychen@microsoft.com>

lib/helpers.js

@@ -25,7 +25,6 @@
 'use strict';
 
 var _ = require('lodash');
-var cloneDeep = require('clone-deep');
 var formatGenerators = require('./validation/format-generators');
 var formatValidators = require('./validation/format-validators');
 var customValidators = require('./validation/custom-zschema-validators');
@@ -471,10 +470,6 @@ module.exports.removeCirculars = function (obj) {
  * @returns {object} Object containing the errors and warnings of the validation
  */
 module.exports.validateAgainstSchema = function (validator, schema, value, schemaPath, isResponse, options) {
-  // Clone the schema as z-schema alters the provided document (https://github.com/zaggino/z-schema/issues/160#issuecomment-214901835). 
-  // Original lodash's deep clone was used but during memory profiling we've found lodash's deep clone takes a lot of CPU, according to this benchmark (https://github.com/ahmadnassri/benchmark-node-clone) and load testing, we've decided to replace lodash with this deep-clone library
-  schema = cloneDeep(schema); 
-
   var response = {
     errors: [],
     warnings: []