fix: simplify SetBackgroundColor

The compositor_superview member of BridgedNativeWidgetMac has been removed so as a consequence there is only one layer on which we need to call setBackgroundColor

atom/browser/native_window_mac.mm

@@ -999,13 +999,7 @@ bool NativeWindowMac::IsKiosk() {
 void NativeWindowMac::SetBackgroundColor(SkColor color) {
   base::ScopedCFTypeRef<CGColorRef> cgcolor(
       skia::CGColorCreateFromSkColor(color));
-  // views::Widget adds a layer for the content view.
-  auto* bridge = views::NativeWidgetMac::GetBridgeForNativeWindow(window_);
-  auto* compositor_superview = bridge->ns_view();
-  [[compositor_superview layer] setBackgroundColor:cgcolor];
-  // When using WebContents as content view, the contentView also has layer.
-  if ([[window_ contentView] wantsLayer])
-    [[[window_ contentView] layer] setBackgroundColor:cgcolor];
+  [[[window_ contentView] layer] setBackgroundColor:cgcolor];
 }
 
 void NativeWindowMac::SetHasShadow(bool has_shadow) {