Revert "Allow setting of TestWidgetsFlutterBinding.pointerEventSource (#107976)" (#108038)

This reverts commit 641f4e24.

packages/flutter_test/lib/src/binding.dart

@@ -494,7 +494,8 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   ///
   /// When [handlePointerEvent] is called directly, [pointerEventSource]
   /// is [TestBindingEventSource.device].
-  TestBindingEventSource pointerEventSource = TestBindingEventSource.device;
+  TestBindingEventSource get pointerEventSource => _pointerEventSource;
+  TestBindingEventSource _pointerEventSource = TestBindingEventSource.device;
 
   /// Dispatch an event to the targets found by a hit test on its position,
   /// and remember its source as [pointerEventSource].
@@ -529,12 +530,12 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   /// to the previous value.
   @protected
   void withPointerEventSource(TestBindingEventSource source, VoidCallback task) {
-    final TestBindingEventSource previousSource = pointerEventSource;
-    pointerEventSource = source;
+    final TestBindingEventSource previousSource = _pointerEventSource;
+    _pointerEventSource = source;
     try {
       task();
     } finally {
-      pointerEventSource = previousSource;
+      _pointerEventSource = previousSource;
     }
   }
 

packages/flutter_test/test/bindings_test.dart

@@ -31,11 +31,6 @@ void main() {
       binding.defaultTestTimeout = const test_package.Timeout(Duration(minutes: 5));
       expect(binding.defaultTestTimeout.duration, const Duration(minutes: 5));
     });
-
-    test('allows setting pointerEventSource to TestBindingEventSource.test', () {
-      binding.pointerEventSource = TestBindingEventSource.test;
-      expect(binding.pointerEventSource, TestBindingEventSource.test);
-    });
   });
 
   // The next three tests must run in order -- first using `test`, then `testWidgets`, then `test` again.