1. `origin-url` was introduced in the past when there was no good
framework support to detect current host url
* It is not needed anymore
* Removing it makes the code clearer
2. Separate template helper functions for different templates (web
page/mail)
3. The "AppURL" info is removed from admin config page: it doesn't
really help.
* We already have various app url checks at many places
Current template uses the owner followed by the instance URL as the repo
name. Technically this can work if the repo happens to be named the
exact same way. But if, for example, you follow [the
docs](https://docs.gitea.com/usage/packages/arch/#publish-a-package),
you'll end up with a package in `core` while the pacman conf refers to a
non-existent repo `testuser.gitea.example.com`. Whatever is in the
square brackets get substituted in for `$repo`, so we do not want
anything except the exact repo name there.
And since it's now referring to the repo and not the owner, I've updated
the pacman conf to show all repositories.
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Co-authored-by: Giteabot <teabot@gitea.io>
