To solve this issue I looked at the <publishDate/> configuration option in the site descriptor, but the only documented options for specifying the date location are left, right, navigation-top, navigation-bottom, and bottom. There is no option to simply disable the date being inserted in the document.
Looking at the default page template I however noticed that it's possible to trick the site not to include the publish date by using a dummy location like "none":
Works for me. :-) I also requested documenting this to avoid the hack getting broken in some future Maven version.