The population of ETC is dependent on the resource's allocation % on the project. In order for a resource to not have ETC Auto assigned to a task, the resource allocation must be 0% during the time period of the task assignment.
If allow effort task creation is set in PPM, ETCs will be generated automatically for resources once they are added to the project if their allocation is >0%. See KB 53503 for more details on what the effort Task is and how is ETC calculated on it.
If you want to prevent ETCs from being auto assigned to a resource, ensure the user's allocation is 0% on the project prior to assigning the resource to the task (and if using effort tasks, set default allocation for resources to 0%).
See KB:35674 for steps on how to change the default allocation for all resources added to projects to 0%.
If you want to remove ETCs for a resource that were added, this would be done at the task assignment level.