Fix F5 experience in VS for crossgen2 (dotnet/coreclr#27104)

Fix F5 experience in VS for crossgen2 (dotnet/coreclr#27104)

Ever since dotnet/coreclr#26792 I wasn't able to F5 launch the crossgen2 project from the src\tools\crossgen2\crossgen2.sln solution. I tried git clean, updating VS, etc. until I convinced myself this is really broken for everyone.

The error was:

```
It was not possible to find any compatible framework version
The specified framework 'Microsoft.NETCore.App', version '3.0.0' was not found.
  - No frameworks were found.
```

I narrowed this down to the various json config file gunk. Not generating the json file gunk makes the old setup work again. We likely don't need the crossgen2/libs hack anymore either.

Commit migrated from https://github.com/dotnet/coreclr/commit/088299e2b7f439dfd1f5056fdc291b9d82149fc1