DS console cake unification

and cleanup

- In both Core and App versions some variables have been unsetted that didnt even exist.
- I also unified DS the same way it is for [index.php](https://github.com/cakephp/cakephp/blob/master/app/webroot/index.php#L24) and test.php since it used later anyway, as well.

- Added the missing `unset($rootInstall, $composerInstall);` part.