Remove unnecessary null checks in integration_test (#118861)

packages/integration_test/lib/integration_test.dart

@@ -252,7 +252,6 @@ https://flutter.dev/docs/testing/integration-tests#testing-on-firebase-test-lab
     @visibleForTesting vm.VmService? vmService,
     @visibleForTesting HttpClient? httpClient,
   }) async {
-    assert(streams != null);
     assert(streams.isNotEmpty);
     if (vmService != null) {
       _vmService = vmService;

packages/integration_test/lib/integration_test_driver.dart

@@ -35,7 +35,6 @@ Future<void> writeResponseData(
   String testOutputFilename = 'integration_response_data',
   String? destinationDirectory,
 }) async {
-  assert(testOutputFilename != null);
   destinationDirectory ??= testOutputsDirectory;
   await fs.directory(destinationDirectory).create(recursive: true);
   final File file = fs.file(path.join(