keybindings: Remove support for 'panel-main-menu' binding

Nothing uses it anymore, and probably nobody expects mutter to
send an X11 client message to gnome-panel in that case.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1886>

src/core/keybindings.c

@@ -3169,9 +3169,6 @@ handle_panel (MetaDisplay     *display,
   switch (action)
     {
       /* FIXME: The numbers are wrong */
-    case META_KEYBINDING_ACTION_PANEL_MAIN_MENU:
-      action_atom = x11_display->atom__GNOME_PANEL_ACTION_MAIN_MENU;
-      break;
     case META_KEYBINDING_ACTION_PANEL_RUN_DIALOG:
       action_atom = x11_display->atom__GNOME_PANEL_ACTION_RUN_DIALOG;
       break;
@@ -3971,13 +3968,6 @@ init_builtin_key_bindings (MetaDisplay *display)
                           META_KEYBINDING_ACTION_SHOW_DESKTOP,
                           handle_show_desktop, 0);
 
-  add_builtin_keybinding (display,
-                          "panel-main-menu",
-                          common_keybindings,
-                          META_KEY_BINDING_NONE,
-                          META_KEYBINDING_ACTION_PANEL_MAIN_MENU,
-                          handle_panel, META_KEYBINDING_ACTION_PANEL_MAIN_MENU);
-
   add_builtin_keybinding (display,
                           "panel-run-dialog",
                           common_keybindings,

src/meta/prefs.h

@@ -268,7 +268,6 @@ int      meta_prefs_get_drag_threshold (void);
  * @META_KEYBINDING_ACTION_CYCLE_PANELS: FILLME
  * @META_KEYBINDING_ACTION_CYCLE_PANELS_BACKWARD: FILLME
  * @META_KEYBINDING_ACTION_SHOW_DESKTOP: FILLME
- * @META_KEYBINDING_ACTION_PANEL_MAIN_MENU: FILLME
  * @META_KEYBINDING_ACTION_PANEL_RUN_DIALOG: FILLME
  * @META_KEYBINDING_ACTION_TOGGLE_RECORDING: FILLME
  * @META_KEYBINDING_ACTION_SET_SPEW_MARK: FILLME
@@ -366,7 +365,6 @@ typedef enum _MetaKeyBindingAction
   META_KEYBINDING_ACTION_CYCLE_PANELS,
   META_KEYBINDING_ACTION_CYCLE_PANELS_BACKWARD,
   META_KEYBINDING_ACTION_SHOW_DESKTOP,
-  META_KEYBINDING_ACTION_PANEL_MAIN_MENU,
   META_KEYBINDING_ACTION_PANEL_RUN_DIALOG,
   META_KEYBINDING_ACTION_TOGGLE_RECORDING,
   META_KEYBINDING_ACTION_SET_SPEW_MARK,

src/x11/atomnames.h

@@ -66,7 +66,6 @@ item(_GTK_EDGE_CONSTRAINTS)
 item(_GTK_WORKAREAS)
 item(_GNOME_WM_KEYBINDINGS)
 item(_GNOME_PANEL_ACTION)
-item(_GNOME_PANEL_ACTION_MAIN_MENU)
 item(_GNOME_PANEL_ACTION_RUN_DIALOG)
 item(_MUTTER_TIMESTAMP_PING)
 item(_MUTTER_FOCUS_SET)