Django will include django.contrib.auth in INSTALLED_APPS, which means User and Groups models are included in admin automatically.
_images/remove_default_apps.png
If you want to remove it, you will have to unregister them.
from django.contrib.auth.models import User, Group


admin.site.unregister(User)
admin.site.unregister(Group)
After making these changes, your admin should look like this.
_images/remove_default_apps_fixed.png