remove --trace-startup (#66568)

dev/devicelab/lib/tasks/perf_tests.dart

@@ -38,6 +38,7 @@ TaskFunction createUiKitViewScrollPerfTest() {
     'test_driver/uikit_view_scroll_perf.dart',
     'platform_views_scroll_perf',
     testDriver: 'test_driver/scroll_perf_test.dart',
+    needsFullTimeline: false,
   ).run;
 }
 

dev/devicelab/manifest.yaml

@@ -506,7 +506,6 @@ tasks:
       Measures the runtime performance of platform views in the Complex Layout sample app on iPhone 6.
     stage: devicelab_ios
     required_agent_capabilities: ["mac/ios"]
-    flaky: true
 
   flutter_gallery_ios32__start_up:
     description: >