build: webpack - warning "PurifyPlugin is deprecated and will be removed in 0.7.0"

[christophercr]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[X] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#got-a-question-or-problem

Current behavior

A warning is displayed when running the application with webpack on DEV:

WARNING in PurifyPlugin is deprecated and will be removed in 0.7.0

Such warning was introduced in this commit: angular/devkit@cb2703e

Expected behavior

No warnings during webpack builds.

Minimal reproduction of the problem with instructions

Run npm start in the showcase or the starter.

What is the motivation / use case for changing the behavior?

Environment

Angular version: 6.1.x

[christophercr]

Apparently the PurifyPlugin is deprecated in Angular 6.1.x because Webpack 4 provides the same functionality as this plugin and its TS transformer.

We need to check and see if they provide some guidelines on how to configure Webpack to achieve the same functionality of this plugin.

[christophercr]

The PurifyPlugin is finally removed in Angular 7 because it is no longer needed as with Webpack 4 and its built-in module concatenation plugin..
See https://github.com/angular/angular-cli/pull/12171/files and angular/angular-cli#12194

So it seems we could just remove the plugin from our webpack config since we are using Angular 6.1.x (no need to wait until we upgrade to Angular 7).