Remove flutter_gallery_ios32__transition_perf test (#65415)

dev/devicelab/bin/tasks/flutter_gallery_ios32__transition_perf.dart

-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:async';
-
-import 'package:flutter_devicelab/tasks/gallery.dart';
-import 'package:flutter_devicelab/framework/adb.dart';
-import 'package:flutter_devicelab/framework/framework.dart';
-
-Future<void> main() async {
-  deviceOperatingSystem = DeviceOperatingSystem.ios;
-  await task(createGalleryTransitionTest());
-}

dev/devicelab/manifest.yaml

@@ -486,14 +486,6 @@ tasks:
     stage: devicelab_ios
     required_agent_capabilities: ["mac/ios32"]
 
-  flutter_gallery_ios32__transition_perf:
-    description: >
-      Measures the performance of screen transitions in Flutter Gallery on
-      32-bit iOS (iPhone 4S).
-    stage: devicelab_ios
-    required_agent_capabilities: ["mac/ios32"]
-    flaky: true
-
   flavors_test_ios:
     description: >
       Checks that flavored builds work on iPhone 6.