Steam OSS' RegisterServerLink causes include of private header resulting in compile error

Hi,

Thank you for bringing this to our attention! This seems to be an oversight with including OnlineSubsystemSteamPrivate.h in OnlinePurchaseInterfaceSteam.h, and I’ve opened a new issue for this, UE-273830, which should be visible in the public tracker in a day or so.

Thanks,

Alex