Remove implementations for X-Admin-Request

[Noroth]

In order to perform admin calls, we added an additional security layer to the authorization. The service requires the header X-Admin-Request to be set with the constant value available

This header is set from the legacy regsys classic.

Once the identity provider supports 2FA we have to remove the implementations within the service.

Hint: Searching for:
// See reference https://github.com/eurofurence/reg-payment-service/issues/57

Should locate all code sections, which have to be removed.

[Jumpy-Squirrel]

Already removed this in the room-service (which does not expose highly sensitive data). By the same argument, we can remove all checks for this header from this service.

Keep in mind that it will stay in the attendee-service for now, so admin requests sent TO the attendee service will still need it.