Reverts "[Impeller] Make impeller goldens test blocking. (#143864)" (#143896)

Reverts flutter/flutter#143864

Initiated by: goderbauer

Reason for reverting: The test is consistently failing in post-submit, e.g. https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8755443299639610049/+/u/run_test.dart_for_framework_tests_shard_and_subshard_impeller/stdout

Original PR Author: jonahwilliams

Reviewed By: {matanlurey}

This change reverts the following previous change:
Original Description:
Part of https://github.com/flutter/flutter/issues/143616

Without this these tests only run on postsubmit which means we can't get gold results on PRs.

.ci.yaml

@@ -3460,6 +3460,7 @@ targets:
   - name: Mac framework_tests_impeller
     recipe: flutter/flutter_drone
     timeout: 60
+    bringup: true
     properties:
       cpu: x86 # https://github.com/flutter/flutter/issues/119880
       dependencies: >-