Retire fileinfo and imageinfo pages

[marktsuchida]

These are pages imported from the MediaWiki File: URLs, and typically contain a description for the file and image.

• Any of these pages that contain a long description should probably have its content moved to an appropriate ordinary page.
• Image pages with short descriptions should be removed, but the description should generally be moved to the alt of where the image is used.
• Non-image file pages whose description has something to add should have its content edited into the page linking to the file. Those that only have a trivial sentence can just be deleted, if not linked from anywhere.