feat(panel-menu): remove duplicate in fullscreen

closes #4064

public/app/features/panel/panel_ctrl.ts

@@ -96,7 +96,9 @@ export class PanelCtrl {
     let menu = [];
     menu.push({text: 'View', click: 'ctrl.viewPanel(); dismiss();'});
     menu.push({text: 'Edit', click: 'ctrl.editPanel(); dismiss();', role: 'Editor'});
-    menu.push({text: 'Duplicate', click: 'ctrl.duplicate()', role: 'Editor' });
+    if (!this.fullscreen) { //  duplication is not supported in fullscreen mode
+      menu.push({ text: 'Duplicate', click: 'ctrl.duplicate()', role: 'Editor' });
+    }
     menu.push({text: 'Share', click: 'ctrl.sharePanel(); dismiss();'});
     return menu;
   }