Remove some ignores for un-deprecated imports (#125261)

The latest version of `test_api` removed the deprecated annotation for a couple libraries. The deprecations had been a hack to avoid usage from inappropriate places, but they cause trouble and likely weren't effective for that goal.

Remove separate import for `registerException` since that was also moved to be available from the top level `scaffolding.dart` library.

packages/flutter_test/lib/src/widget_tester.dart

@@ -49,11 +49,8 @@ export 'package:matcher/expect.dart' hide expect, isInstanceOf;
 // The test_api package has a deprecation warning to discourage direct use but
 // that doesn't apply here.
 export 'package:test_api/hooks.dart' show TestFailure;
-// ignore: deprecated_member_use
 export 'package:test_api/scaffolding.dart'
     hide group, setUp, setUpAll, tearDown, tearDownAll, test;
-// ignore: implementation_imports
-export 'package:test_api/src/scaffolding/utils.dart' show registerException;
 
 /// Signature for callback to [testWidgets] and [benchmarkWidgets].
 typedef WidgetTesterCallback = Future<void> Function(WidgetTester widgetTester);

packages/flutter_tools/lib/src/test/test_wrapper.dart

@@ -8,7 +8,7 @@ import 'package:test_core/src/executable.dart' as test; // ignore: implementatio
 import 'package:test_core/src/platform.dart' as hack show registerPlatformPlugin; // ignore: implementation_imports
 import 'package:test_core/src/platform.dart'; // ignore: implementation_imports
 
-export 'package:test_api/backend.dart' show Runtime; // ignore: deprecated_member_use
+export 'package:test_api/backend.dart' show Runtime;
 export 'package:test_core/src/platform.dart' show PlatformPlugin;
 
 abstract class TestWrapper {