Revert "Fixes Setting BackgroundColor to null does not actually changes BackgroundColor #22914 (#22917)" (#30031)

This reverts commit 19402d3.

Author: mattleibow

src/Controls/tests/TestCases.HostApp/Issues/Issue22914.xaml

@@ -300,7 +300,7 @@ internal static void UpdateBackground(this AView platformView, Paint? background
 						platformView.Background = drawable;
 				}
 			}
-			else if (platformView is not null)
+			else if (platformView is LayoutViewGroup)
 			{
 				platformView.Background = null;
 			}

src/Controls/tests/TestCases.HostApp/Issues/Issue22914.xaml.cs

@@ -77,7 +77,7 @@ public static void UpdateBackground(this UIView platformView, Paint? paint, IBut
 
 			if (paint.IsNullOrEmpty())
 			{
-				if (platformView is not null)
+				if (platformView is LayoutView)
 					platformView.BackgroundColor = null;
 				else
 					return;