Removed overrides from Gruntfile.js

- nothing in Gruntfile.js uses bluebird or mocha
- they ARE seperately required by mocha-cli ahead of our tests in the config

Gruntfile.js

@@ -5,9 +5,6 @@
 // **Usage instructions:** can be found in the [Custom Tasks](#custom%20tasks) section or by running `grunt --help`.
 //
 // **Debug tip:** If you have any problems with any Grunt tasks, try running them with the `--verbose` command
-
-require('./core/server/overrides');
-
 const config = require('./core/shared/config');
 const urlService = require('./core/frontend/services/url');
 const _ = require('lodash');