Remove obsolete iOS benchmark (#126862)

Fixes https://github.com/flutter/flutter/issues/126861

.ci.yaml

@@ -3799,15 +3799,6 @@ targets:
         ["devicelab", "ios", "mac"]
       task_name: new_gallery_skia_ios__transition_perf
 
-  - name: Mac_ios ios_picture_cache_complexity_scoring_perf__timeline_summary
-    recipe: devicelab/devicelab_drone
-    presubmit: false
-    timeout: 60
-    properties:
-      tags: >
-        ["devicelab", "ios", "mac"]
-      task_name: ios_picture_cache_complexity_scoring_perf__timeline_summary
-
   - name: Mac_ios platform_channel_sample_test_ios
     recipe: devicelab/devicelab_drone
     presubmit: false

dev/devicelab/bin/tasks/ios_picture_cache_complexity_scoring_perf__timeline_summary.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 'package:flutter_devicelab/framework/devices.dart';
-import 'package:flutter_devicelab/framework/framework.dart';
-import 'package:flutter_devicelab/tasks/perf_tests.dart';
-
-Future<void> main() async {
-  deviceOperatingSystem = DeviceOperatingSystem.ios;
-  await task(createPictureCacheComplexityScoringPerfTest());
-}