Don't send live sector tags out to Rummager.

It's OK for us to send these into the content store
as it's impossible to subscribe to a draft tag and
in the future the draft tags will be stripped by
the content store once they're moved to the `links`
hash.
Merge pull request #1858 from alphagov/dont-send-draft-tags-out-of-whitehall

Don't send draft sector tags out to Rummager.