Replace collection data in /api/v1/search/featured/ by empty arrays (bug 1058292)

Also simplify fireplace variant now that yogafire - which doesn't care
about collections at all - is the only client left using it, and mark
/api/v2/search/featured/ as removed.
Merge pull request #2621 from diox/remove-featured

Replace collection data in /api/v1/search/featured/ by empty arrays (bug 1058292)