chore: remove mpris slot from snapcraft to unblock Snap Store review

The mpris slot requires an auto-connect review from Canonical that has
been pending for 9+ days. Remove it to unblock the version bump from
1.1.18 to 1.1.20. MPRIS media controls will not work in the snap
build until the review is approved in a future release.

cc

snapcraft.yaml

@@ -81,13 +81,6 @@ apps:
       - gsettings
       - alsa
       - pipewire
-    slots:
-      - mpris-player
-
-slots:
-  mpris-player:
-    interface: mpris
-    name: qbz
 
 parts:
   qbz: