(responding to Ed)
> So, the 28 is no longer being used and can be removed.
Done.

> Since you're at F30 you should also have a /var/cache/PackageKit/30 directory structure
> which is now being used.

I don't have it.  This might relate to actions taken in my December 2018 thread "unwanted checks for updates".  I'd like confirmation that I don't have a problem here.

> /var/cache/abrt-di/usr
> That most likely contains a bunch of core files that are no longer needed.
That directory looks huge and complex.  I saw lots of links and lots of source code (".c" and ".h" files).  Would you like me to fpaste a recursive long list (ls -alR) of it?

> The key to getting good answers is to ask good questions.
Agreed, but it can be surprisingly difficult sometimes to figure out what the good questions are!  Reminds me of a professor in a class asking if there were any questions.  When there were none, he commented he guessed we didn't know enough to know what to ask!

thanks,
Bill.