Move the hosting sample on level up

[vitek-karas]

In a recent change the second hosting sample was removed, so there's only one now. No point in keeping it in a subdirectory.

Also updated the readme to talk about ".NET" instead of ".NET Core" where appropriate.

[vitek-karas]

@BillWagner could you please help me determine what's wrong here? It says:

Project missing. A project (and optionally a solution file) must be in this directory or one of the parent directories to validate and build this code.

But I don't know which directory it's talking about. Based on the output json I can only guess it's about global.json which is one directory higher than the solution, but it has a project file right next to it. And this change only moves the entire structure, I made no functional changes...

[BillWagner]

@vitek-karas I think this is a false positive (and we can merge this even with the build failure).

Our samples build scripts detect that source code was changed, so some project should be rebuilt. In this PR, the source code and the project was removed, so that folder doesn't need to be rebuilt. (That check is in place to catch if we remove source that's needed in a sample by mistake.).

Adding @adegeo

I think we need to add a path for removed source code to allow removing all source for a folder project.

[vitek-karas]

Thanks a lot @BillWagner - I'll merge it.