panel: Dispose unneeded menu
panel: Dispose unneeded menu

..and correctly re-parent actions.

lxde/lxqt-panel,lxde/lxqt-panel,stefonarch/lxqt-panel,stefonarch/lxqt-panel,pmattern/lxqt-panel,stefonarch/lxqt-panel,pmattern/lxqt-panel