Fixes T12281. Some forms (like Settings) can't actually create new objects. Currently, though, you can select them and add them to profile menus; if you do, they fail when building an item.

Kick them out of the typeahead, and decline to render them in menus.

Added "Create Settings" to a menu, no longer fatals after patch (item vanished from menu, still editable normally to get rid of it).

Tried to add another "Create Settings", no longer available in typehaead.

Added some normal stuff.

Viewed a choose-among-forms dropdown in Maniphest, which still worked normally.