Oracle: deleting all services associated with a SID
SYS$BACKGROUND and SYS$USERS are built-in internal services, they are not exposed to the listener and clients.

XE is your default service, because an Oracle database by default has a service with its db_unique_name, and registers itself to a listener running on the default port (1521) with the db_unique_name as service name, and instance_name as instance.

The XEXDB service exists, because you have the XML database option configured, and the dispatchers parameter is set.

You do not need to modify service_names manually, the database handles that parameter based on the service configuration.

In my opinion, the use of services should be promoted, not prevented. Using multiple services for a single database has the benefit of being able to manage clients connecting through different services seperately, when troubleshooting (tracing), or prioritizing workload (resource manager).