refactor: Simplify themes and remove dead code

lib/pages/settings_style/settings_style.dart

@@ -44,8 +44,8 @@ class SettingsStyleController extends State<SettingsStyle> {
         );
     AppConfig.colorSchemeSeed = color;
     AdaptiveTheme.of(context).setTheme(
-      light: FluffyThemes.light(),
-      dark: FluffyThemes.dark(),
+      light: FluffyThemes.buildTheme(Brightness.light),
+      dark: FluffyThemes.buildTheme(Brightness.dark),
     );
   }