Fix UNNECESSARY_TYPE_CHECK_TRUE violations. (#89186)

dev/bots/test.dart

@@ -455,9 +455,6 @@ Future<void> _runBuildTests() async {
 Future<void> _runExampleProjectBuildTests(Directory exampleDirectory, [File? mainFile]) async {
   // Only verify caching with flutter gallery.
   final bool verifyCaching = exampleDirectory.path.contains('flutter_gallery');
-  if (exampleDirectory is! Directory) {
-    return;
-  }
   final String examplePath = exampleDirectory.path;
   final bool hasNullSafety = File(path.join(examplePath, 'null_safety')).existsSync();
   final List<String> additionalArgs = <String>[

dev/devicelab/lib/framework/manifest.dart

@@ -107,7 +107,6 @@ List<ManifestTask> _validateAndParseTasks(dynamic tasksYaml) {
 }
 
 ManifestTask _validateAndParseTask(String taskName, dynamic taskYaml) {
-  _checkType(taskName is String, taskName, 'Task name', 'string');
   _checkType(taskYaml is YamlMap, taskYaml, 'Value of task "$taskName"', 'dictionary');
   _checkKeys(taskYaml as YamlMap, 'Value of task "$taskName"', const <String>[
     'description',