Remove highContrast from FakeAccessibilityFeatures (#51130)

packages/flutter_test/test/window_test.dart

@@ -256,7 +256,6 @@ class FakeAccessibilityFeatures implements AccessibilityFeatures {
     this.disableAnimations = false,
     this.boldText = false,
     this.reduceMotion = false,
-    this.highContrast = false,
   });
 
   @override
@@ -274,11 +273,12 @@ class FakeAccessibilityFeatures implements AccessibilityFeatures {
   @override
   final bool reduceMotion;
 
-  final bool highContrast;
-
   /// This gives us some grace time when the dart:ui side adds something to
   /// [AccessibilityFeatures], and makes things easier when we do rolls to
   /// give us time to catch up.
+  ///
+  /// If you would like to add to this class, changes must first be made in the
+  /// engine, followed by the framework.
   @override
   dynamic noSuchMethod(Invocation invocation) {
     return null;