wizard: reimplement system setup and remove openvpn server one

[fichtner]

Important notices

Before you add a new report, we ask you kindly to acknowledge the following:

• I have read the contributing guide lines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues at https://github.com/opnsense/core/issues?q=is%3Aissue

Is your feature request related to a problem? Please describe.

The wizard works on XML files which we have tolerated for OpenVPN server and initial setup, but never did more than fix bugs and avoid the code as much as possible.

Describe the solution you like

Remove the wizard.php and related glue from the project and build a lightweight form for the wizard steps.

Describe alternatives you considered

No. This needs to go.

Additional context

#8347