Remove isSidebarVisible field from DemosMainLayout

The field `isSidebarVisible` of type `bool` was removed from the `DemosMainLayout` class. This field was previously initialized to `false`, indicating that the sidebar was not visible by default.

NOTE: This commit message is auto-generated using GitHub Copilot.

Author: gvreddy04

BlazorExpress.Bulma.Demo.RCL/Layout/DemosMainLayout.razor.cs

@@ -4,7 +4,6 @@ public partial class DemosMainLayout : MainLayoutBase
 {
     #region Fields and Constants
 
-    private bool isSidebarVisible = false;
     private HashSet<LinkGroup> linkGroups = new();
     private Menu menuRef = default!;