Yes it worked fine.
I did dangerous operation and deleted all Tracks. Now in dashboard tracks I can see no more tracks.
The folders /srv/airtime/stor/imported/ was still keeping the empty folders.
sudo rm -r /srv/airtime/stor/imported/* cleaned all.
Now I can start again importing tracks, but I think this is not a general good solution.
I think it needs in the end of deleting tracks procedure the command to delete empty folders too.
Same like it’s done in EasyBrainz Picard. (I’m working with Xubuntu 16.04 and Libretime-Master)