On Mac, 3.5.19, I couldn’t get rid of a watched folder and it’s tracks. Removing the folder from the UI removes it from the visible list, but it stays in the sqlite db, as do all the tracks. The tracks remain in the db and browsable even if the whole directory goes away, even if you attempt playback, even after you check/reindex/defrag the db…
Workaround… Well, I stopped Audirvana and used sqlite3:
delete from WATCHED_FOLDERS where relative_path = 'go_away';
delete from TRACKS where location_rel_path like 'go_away/%';
…gone, bye-bye. 