tracker-utilities: Ignore XDG use dirs set to $HOME

If the "index-recursive-directory" key lists an XDG user dir which is
set to $HOME (e.g., in my case, I have no Desktop folder), then we
assume the whole home dir is recursively indexed. As a result, we
show stars everywhere under the home dir.

But this is not what Tracker's files miner does. It ignores these
cases, avoiding recursively indexing the whole home dir.

So, skip these cases. Also, document the utility function.
4 jobs for 947-impossible-to-star-files-in-subfolders in 11 minutes and 59 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #315888
flatpak devel

00:10:52

failed #315885
flatpak devel

00:00:15

 
  Deploy
passed #315886
review

00:01:06

manual #315887
allowed to fail manual
stop_review