[ticket/12534] Do not abuse errorbox for en/disable confirmation of extensions

Delete data is kept red, as that is what is really dangerous in some cases

https://tracker.phpbb.com/browse/PHPBB3-12534

Before:
![before](https://cloud.githubusercontent.com/assets/213943/2942305/a43c3988-d9b2-11e3-868d-5bb52db60b75.png)

After:
![after](https://cloud.githubusercontent.com/assets/213943/2942306/a5c53f70-d9b2-11e3-8ec6-c6fb23b20f19.png)