Remove need for polkit, launch any ArchUpdater update through terminal

ArchUpdater: rely on `TERMINAL` environment variable
README: Add explanation for the `TERMINAL` environment variable

Modules/Bar/Widgets/ArchUpdater.qml

@@ -64,6 +64,5 @@ NIconButton {
 
     PanelService.getPanel("archUpdaterPanel").toggle(screen, this)
     ArchUpdaterService.doPoll()
-    ArchUpdaterService.doAurPoll()
   }
 }