Those attachment point references can be deleted from the config.txt file. Open the asset for edit with a finder window, if that's what the folders and files explorer is called on the mac, in your content manager. When you can see the files and folders, look for config.txt and then delete those lines. There is no need to adjust any reference numbers next to them; just delete the broken ones.
Once all this done, save the file, close the folders, and back in content manager, check for errors again. You should be all set.
John