Summary: Ref T10923. Currently, users can disable or enable builtin URIs, but this doesn't actually do anything. The behavior of "disable" has changed a bit over time and might need some further refinement, but it's currently meaningless for builtin URIs. Prevent adjustment of it. If users want to hide a URI, they should set "Display: Hidden" instead. Test Plan: - Disabled/enabled a non-builtin URI. - Tried to disable a builtin URI, saw greyed out UI and got a helpful error message. Reviewers: chad Reviewed By: chad Subscribers: eadler Maniphest Tasks: T10923 Differential Revision: https://secure.phabricator.com/D15899