SEO: Remove itemprop='datePublished' from all content trails

This removes the datePublished schema attribute from all facia/container trails, as per adivce from the SEO team. 

From Joost:

"There are itemprop=datePublished attributes on related articles, this might cause havoc as it now seems Google is unable to correctly parse the date published:

http://www.google.com/webmasters/tools/richsnippets?url=http://www.theguardian.com/film/2014/may/14/grace-of-monaco-cannes-review-nicole-kidman?view=mobile

For now my suggestion be to remove the itemprop, as it seems there is no proper way to define that something is a related article with schema.org yet."

/cc @gklopper