Clean up CentralNotice Translation Metadata

Right now the translation metadata job is running very slowly --
part of this problem is that there is a lot of junk metadata
that we have to process.

So... the maintenance script cleans things up. And I'm now putting
the banner id in with the revtag object so that we can eventually
look to see if the banner is archived or attached only to archived
campaigns or something.

E.g. this patch alone will take 800 objects on meta down to ~250.

Bug: 53769
Bug: 53792
Change-Id: If9ae70977ee0f008f65ef8f742acafb991b4d221
Merge "Clean up CentralNotice Translation Metadata"