Marks Linux_android slider_perf_android to be unflaky (#125968)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Linux_android slider_perf_android"
}
-->
The test has been passing for [50 consecutive
runs](https://data.corp.google.com/sites/flutter_infra_metrics_datasite/flutter_check_test_flakiness_status_dashboard/?p=BUILDER_NAME:%22Linux_android%20slider_perf_android%22).
This test can be marked as unflaky.

.ci.yaml

@@ -2242,7 +2242,6 @@ targets:
       task_name: android_picture_cache_complexity_scoring_perf__timeline_summary
 
   - name: Linux_android slider_perf_android
-    bringup: true
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60