Revert "Marks Linux_pixel_7pro service_extensions_test to be flaky" (#163882)

Reverts flutter/flutter#157853

Should have fixed flutter/flutter#157852 but
that was closed.

Author: jmagman

.ci.yaml

@@ -3253,7 +3253,6 @@ targets:
       task_name: routing_test
 
   - name: Linux_pixel_7pro service_extensions_test
-    bringup: true # Flaky https://github.com/flutter/flutter/issues/157852
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60