panel: Remove the appMenu indicator

Over time the app menu has proved to be an issue and lately there has been
some movement to fix that (see also
https://gitlab.gnome.org/Teams/Design/os-mockups/-/issues/198).

As a first step, let's stop showing the indicator (not removing the code
yet) so that we can iterate on a more elegant solution.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2610>

js/ui/sessionMode.js

@@ -92,7 +92,7 @@ const _modes = {
         unlockDialog: imports.ui.unlockDialog.UnlockDialog,
         components: USER_SESSION_COMPONENTS,
         panel: {
-            left: ['activities', 'appMenu'],
+            left: ['activities'],
             center: ['dateMenu'],
             right: ['screenRecording', 'screenSharing', 'dwellClick', 'a11y', 'keyboard', 'quickSettings'],
         },