Revert "music: replace Spotify by Deezer"

This reverts commit 4af98c2589. I feel
like they should provide a native client for Linux instead of relying
upon the community. MellowPlayer is unmaintained and does not have an
offline mode. Deezer seems the only streaming service with a Linux
client.

bin/spotify-clean

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+# Kill all spotify streams, except the most recent one.
+
+pactl list short clients \
+    | awk '($3 == "spotify") {print $1}' \
+    | head -n-1 \
+    | xargs -rn1 pacmd kill-client