Fix unit test

Author: SteveSandersonMS

src/Components/Components/test/Routing/RouterTest.cs

@@ -209,8 +209,6 @@ internal class TestNavigationManager : NavigationManager
             public TestNavigationManager() =>
                 Initialize("https://www.example.com/subdir/", "https://www.example.com/subdir/jan");
 
-            protected override void NavigateToCore(string uri, bool forceLoad, bool replace) => throw new NotImplementedException();
-
             public void NotifyLocationChanged(string uri, bool intercepted)
             {
                 Uri = uri;