Forbid portal URL to be a perl expression

Since LL::NG 0.9.4, it is possible in handler and portal config to define portal URL as a perl expression, for example "http://$vhost/auth" (then, $vhost will be replaced with the request hostname, e.g. test1.example.com).

I would like to remove this feature from handler,

• since it is undocumented (well, to be honest it is mentionned on the old wiki)
• since it can be configured only in handler's / portal's config (that is, in PACKAGE->init parameters, and maybe in lemonldap-ng.ini ; but you can't set it in manager : it raises an error)
• since it looks like a screwy feature (I have never had such a need)
• and since I can't keep it if I try to pass apacheRequest as function parameters instead of as global var (needed for ##583 (closed)) - at least, I can't replace $vhost with the request hostname.

By the way, it would allow to simplify code.

Clément, could you give me your opinion / agreement ?