Replace Windows Unopt with the engine v2 version. (flutter#41861)

Both builds have been running successfully. This PR moves Windows Unopt to staging and Windows windows_unopt to prod.

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

.ci.yaml

@@ -526,13 +526,13 @@ targets:
       config_name: windows_arm_host_engine
 
   - name: Windows windows_unopt
-    bringup: true
     recipe: engine_v2/builder
     timeout: 60
     properties:
       config_name: windows_unopt
 
   - name: Windows Unopt
+    bringup: true
     recipe: engine/engine_unopt
     properties:
       add_recipes_cq: "true"