So far the best implementation of "clear query/queue" functionality is coming from Google Play Music. Please implement it in this way Spotify. How is this still not even something you've attempted to implement? I've seen the previous so enough already with looking into it.
Updated on 2018-12-25
Hey @FreeQueue, thanks for coming to the Spotify Community!
A similar idea has been posted here: https://community.spotify.com/t5/Live-Ideas/Queue-Clear-Queue-Button/idi-p/4426986
Please add your comments/votes there and reach out here if you need any other help :)