The "Token" Data Source allows you to create new Datablocks on your Databoards. Because of this, the default Token Data Source cannot be deleted. It does not count towards your Data Source limit.
You can push from a custom Data Source to the default Token. However, this could impact performance, so it is recommended that you create a new Token for these purposes. Learn more about creating Token's in Databox and syncing custom data in our Databox Developers Documentation.
If you don't have any Metrics created via Terminal or a custom Data Source pushed to the Token, it will not show up in the Data Source drop-down of Datablock Editor in the Designer.