Remove external link tracking

This was added to get analytics on traffic from specialist guides (now
detailed guidance) to organisation homepages when the organisations
linked in the metadata of those pages were all external. As those links
are all internal this is no longer needed.

Also this way of tracking external links is really very evil.
Add tracking to metadata links

So that we can make smarter decisions about how to change the metadata
patterns some data on usage of metadata links is needed. This adds click
tracking to the metadata links.
Stop listing archived status of detailed guide twice (only once in header)
Merge pull request #1447 from alphagov/track-metadata-links

Add tracking to metadata links
Merge pull request #1449 from alphagov/remove-external-tracking

Remove external link tracking
Merge pull request #1460 from alphagov/archived-banner-bug

Stop listing archived status of detailed guide twice