After all user created data sources have been removed, there is a System data source that appears and can't be deleted.
• When all datasources in Audit are removed, the system creates a data source with test data as the Audit app can't be empty.
Once a System Administrator creates another data source that has successfully parsed data, the system data source is removed.
• Once a datasource is deleted, the previously collected data cannot be recovered unless you create another data source that contains that same data.
https://techdocs.broadcom.com/us/en/symantec-security-software/information-security/symantec-cloudsoc/cloud/audit-home/data-source-management/deleting-a-data-source.html