Hi David, you can remove it using the following:

YourComposer : IUserComposer
{
    composition.Dashboards().Remove<RedirectUrlDashboard>();
}

If you want to restrict the dashboard you will need to create your own that inheirts from the RedirectUrlDashboard and override the AccessRules.

MyRedirectUrlDashboard :  RedirectUrlDashboard
{
    public IAccessRule[] AccessRules => new []
                                        {
                                            new AccessRule {Type = AccessRuleType.Grant, Value = Umbraco.Core.Constants.Security.AdminGroupAlias}
                                        };

}

You would then need to remove the existing and add your new one:

YourComposer : IUserComposer
{
    composition.Dashboards().Remove<RedirectUrlDashboard>()
    .Add<MyRedirectUrlDashboard>();
}

Documentation with the more details can be found here

Thanks

Matt