Forcefully remove obsolete plugin metadata?

After working with the Lightroom SDK for a bit, I've come to realize that deletion is one of the biggest omissions in the SDK.  You can't delete collections, keywords or metadata.  There may be other structures that can't be deleted but those are the ones I've run into off the top of my head.  Of course there are also many constructs that can't be created via the SDK as well but for now, I'm looking at deletion.

I have metadata scattered across my pictures from plugins I no longer use and would like to remove it.  Lightroom doesn't offer a way to do this from the UI or problematically (see Option to remove preferences and metadata for plugin) Since it doesn't appear this is a high priority issue for Adobe (after all, it's been more than 7 years), I'm looking for options on how to forcefully remove this superfluous metadata. I tried exporting a single picture to a new catalog and it drags along all the unneeded metadata. This will obviously get worse as time goes and new metadata being created by plugins.

Is there a way to remove this obsolete metadata from the catalog?  I understand there isn't from the UI and/or SDK but this is a database after all.  Yes, I understand that modifying the database incorrectly could have catastrophic results but I suspect modifying it correctly would not cause a system failure.  Anyone out there study the schema enough to have any suggestions or warnings?