Remove legacy LinkPreview functionality #2023
Description
In LeftAndMain there's a LinkPreview() method which can return a "URL to a previewable record which is shown through this controller". This returns false by default and isn't overridden in any supported module.
This is referenced in LeftAndMain_EditForm.ss and SiteConfigLeftAndMain_EditForm.ss and nowhere else in supported modules. It's immediately before the controls that display when a CMSPreviewable record is managed by the admin section.
This legacy LinkPreview is unused and could lead to unexpected behaviour if used. It should be removed.