It's possible that the /install/.subsonic.lock file is not being removed, for that, I would have to check the uninstaller as it could be a simple edit that I overlooked on the files creation.
Subsonic will continue to be located at
/srv/subsonic/, when mentioned about running as the user this was in regards to subsonic running as
$username and not
subsonic. When the Subsonic service runs as itself it is considered as running as root. This is by no means producing a vulnerable environment, just one of those instances where it feels it necessary to nag you about it.
With that said, check to see that the
/srv/subsonic/ directory has been removed. Additionally, do a
systemctl status subsonic and see if the service is dead. You may also
ps aux|grep subsonic to check for thoroughness. This will help us ensure that it is both being killed as well as the leftover directories purged. If so, then we will simply need to adjust the removal of the leftover