Move cache builders to prod. (flutter#44739)

These builders have been running as bringup for a very long time with no failures.

Bug: flutter#132597

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: godofredoc

.ci.yaml

@@ -115,7 +115,6 @@ targets:
     enabled_branches:
       - main
     recipe: engine_v2/cache
-    bringup: true
     presubmit: false
     properties:
       cache_name: "builder"
@@ -136,7 +135,6 @@ targets:
     enabled_branches:
       - main
     recipe: engine_v2/cache
-    bringup: true
     presubmit: false
     properties:
       cache_name: "builder"
@@ -156,7 +154,6 @@ targets:
     enabled_branches:
       - main
     recipe: engine_v2/cache
-    bringup: true
     presubmit: false
     properties:
       cache_name: "builder"