Remove muon from Lubuntu

muon was removed from Debian unstable in January 2023 with the rationale
that it is abandoned upstream (Debian bug #1029171).  It has not been
removed from Ubuntu because it is seeded in Kubuntu, Lubuntu, and
UbuntuStudio.

I do not know if there is a suitable replacement.

desktop

@@ -128,7 +128,6 @@ Task-Metapackage: lubuntu-desktop
 == Low level system plumbery ==
 
 # Packages management
- * (muon)
  * (plasma-discover)
  * !kde-config-updates              # Possibly dangerous in Lubuntu, causes KDE System Settings to be installed which looks so out of place