Revert r44185, r44186 -- "Foreign repos (API or DB) now fetch images and/or descripti...

Revert r44185, r44186 -- "Foreign repos (API or DB) now fetch images and/or description pages if the repo wiki has a different canonical name for the File: namespace. Added 'fileNamespace' configuration item to $wgForeignFileRepos to override the local canonical name."
The canonical-canonical 'Image' namespace name should always be used here for compatibility; an extra configuration option is unnecessary and adds confusion.