QA: "sidewalk=separate is ambiguous about the side"

What is the check here?
I think we need to consider alle `sidewalk=*` tags the same as `sidewalk:both=*`
There is a long discussion on this in https://github.com/openstreetmap/id-tagging-schema/pull/454#issuecomment-2731787841 and https://github.com/openstreetmap/id-tagging-schema/pull/1507

For both, `cycleway` and `sidewalk`, my current take is to consider them the same as their `:both` variants. I hope to some day convince iD to use the more explicit tagging…

So for this check, I think we can just remove it?

Example https://a-b-street.github.io/speedwalk/#17.22/52.562455/13.052818