As the world moves increasingly to content item and deep linking placements, allowing custom values to be added in a content item is an essential feature. If you set it incorrectly when installing an Deep Linking and Content Item tool, it will simply break in mysterious ways much later.
This will remove the feature, essentially defaulting it to on from this point forward. And it removes a tiny bit of unneeded complexity in our Manage External Tools UI.
This does not need a conversion - the column could be deleted for Sakai-21 - but the column will just be ignored in Sakai-20 if it is there. It can and should be back-ported to Sakai-20 with no conversion necessary.