Remove arguments from RelyingPartyUnvailableError exception

[aequitas]

https://github.com/internetstandards/Internet.nl/blob/main/checks/tasks/routing.py#L324

Passing the HTTP exception as a string to an exception includes a lot of information (eg: the entire url with unique path) in the Sentry issue name, making it unique and filling the Sentry overview with lots of unique entries for the same issue.

Suggest to move this information into an attribute of the exception so it is still available in sentry, but then as events grouped under 1 issue.