chore: update API docs

Author: devvaannsh

docs/API-Reference/view/PanelView.md

@@ -68,12 +68,6 @@ recomputeLayout callback from WorkspaceManager
 ## \_defaultPanelId : <code>string</code> \| <code>null</code>
 The default/quick-access panel ID
 
-**Kind**: global variable  
-<a name="_$addBtn"></a>
-
-## \_$addBtn : <code>jQueryObject</code>
-The "+" button inside the tab overflow area
-
 **Kind**: global variable  
 <a name="_$overflowBtn"></a>