Unmark linux_android platform_channels_benchmarks as flaky (#136838)

Unmarking this test as flaky in favor of a fix for the [underlying issue](https://github.com/flutter/flutter/issues/135035). None of the other impacted tests have been marked as flaky, so I think it is better for this one to not be treated differently.

.ci.yaml

@@ -2539,7 +2539,6 @@ targets:
       task_name: slider_perf_android
 
   - name: Linux_android platform_channels_benchmarks
-    bringup: true # Flaky https://github.com/flutter/flutter/issues/135105
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60