Clean up servicehub projects

We have VSIXManifests in the servicehub.Corecomponents projects that do not appear to actually be used. They are needed for our local tooling to build a VSIX, but the VS machinery doesn't seem to use their content.

Our current build tools don't support arm64 as an install target. Upgrading the build tools brings it own set of issues, so for now, as they aren't used, we just use amd64.

I also think we should rename these project to something like `MS.VS.RazorExtension.ServiceHub` to make it clearer what they actually are. But I think I'll do that in a follow up.

_Originally posted by @chsienki in https://github.com/dotnet/razor/pull/12385#discussion_r2457995810_