Before Mavericks it seems it was easy to make iTunes forget a device as per this question: Can you make iTunes forget a device?
However according to this Apple support article Sync Services doesn't exist anymore in Mavericks
Note: OS X Mavericks does not use Sync Services. Instead, Mavericks supports sharing your information using several network-based and cloud-based solutions. If you want to sync your information across multiple devices and computers, you should use one or more of these methods. These include iCloud, CardDAV servers, CalDAV servers, or servers that use the Exchange ActiveSync protocol.
What is the new trick in Mavericks to make iTunes forget a device?