Exclude WebPreferences pages from the PDF export of page and children, regardless of the preferences of the current user

Today, when exporting a page with all its children, the WebPreferences pages are all exported, under the title of "Page Administration".

The content exported to PDF for those pages seems to be all the same

which is not relevant in any way, in the sense that it doesn't display any information that could be used in any way.

I understand that it's possible to prevent the inclusion of these pages in the PDF by deactivating hidden pages in the profile of the user performing the export, but I think that even if the user would like to export the hidden content, page administration is really not relevant there. We could make this configurable, if anything, at the level of the whole wiki (whether pages administration is exported or not), but I doubt anyone could find this interesting at any point for the pdf export.

This can help make the exports of large page trees lighter, by potentially removing a significant amount of content, that is always the same and irrelevant.