allinkl: remove ReturnInfo

[ldez]

The type of ReturnInfo doesn't seem "stable".

allinkl doesn't have a real API schema: https://kasapi.kasserver.com/soap/wsdl/KasApi.wsdl

<message name="KasApiAntwort">
<part name="Result" type="xsd:anyType"/>
</message>

2025/03/20 12:54:56 [WARN] [*.example.com] acme: cleaning up failed: allinkl: response struct decode: decoding failed due to the following error(s):

'Response.ReturnInfo' expected type '%!s(bool=false)', got unconvertible type '""', value: '""'

Related to #2489

[dmke]

allinkl doesn't have a real API schema

Oh, the schema is real. It's just utterly useless.

[ldez]

Yes it's a real decorative API schema 😄