Remove folders created for service groupings

[jar-stripe]

Why?

The code generator had previously generated pluralized folders for V2 services that only contain other services, like V2/Billings, V2/Cores, V2s, etc. This is undesirable because it produces a confusing directory structure. This PR moves the files out of these folders after modifying the code generator to treat these services like namespaces instead of resource-ful services.

This is not a breaking change as the C# namespaces are not changed.

What?

• moves services out of V2/Cores, and V2/Billings into V2 folder and deletes subfolders
• moves V2Services out of V2S into Stripe.net/Services and removes V2S folder

See also

http://go/j/DEVSDK-2196