Prereqs INCLUDES files have degraded over the years

[guardrex]

While working on the passkeys coverage, I noticed that the INCLUDES files for prereqs have degraded a bit over the years. They're a bit sloppy these days with duplicated/disorganized content and incorrect tooling links. Because the latest SDK compiles prior release targets, there's no need to even have separate SDK-versioned files, especially when they don't have different content to show.

I'll find some time in the coming weeks to address it. I can work with what we have for now in the .NET 10 Migration article, which will be part of the passkeys PR. I won't work this as part of that PR because I don't want to distract the PU at review time for passkeys coverage.

This work will be tracked as a Blazor project item.