Clean up from the move to RC3 packages. Removed the dotnet-core dependency on NuGet.Config now that we have RC3 packages in the cli-deps feed. Re-enabled crossgen for windows now that we added JITPath to the crossgen call.

build_projects/dotnet-cli-build/build.ps1

@@ -35,9 +35,6 @@ else
     $env:DOTNET_BUILD_SKIP_PACKAGING=0
 }
 
-Write-Host "Disabling crossgen for the CLI build. See issue - https://github.com/dotnet/cli/issues/3059"
-$env:DISABLE_CROSSGEN=1
-
 # Load Branch Info
 cat "$RepoRoot\branchinfo.txt" | ForEach-Object {
     if(!$_.StartsWith("#") -and ![String]::IsNullOrWhiteSpace($_)) {