As the `--prod` is now deprecated, and `ng build` uses by default the `production` configuration,
then we should remove the references to `ng build --prod` in the generated project.
Currently when using `ivy-ngcc` it will print out a warning
```
Failed to read entry point info from //node_modules/@schematics/angular/workspace/files/package.json with error SyntaxError: Unexpected token < in JSON at position 1121.
```
Fixes#13378
