Any addon adding such a thing into the Object → Add menue ?? (Since Cablerator is from Blender market …)
You can go to the
Outliner → Display Mode Dropdown → Orphan Data and delete it there.
You can also do this in Display mode → Blend File
Or you can close Blender and restart it.
If the Collection has a fake user you will have to do it in Display Mode → Blend file. But I don’t think collections can have fake users.
Cablerator is one of those add-ons that you think you don’t need…until you DO and you are so grateful you have it.
Thank you @Lumpengnom