Revert "chore: linux fuchsia tests are flaking" (flutter#179897)

Reverts flutter#179744


https://ci.chromium.org/ui/p/flutter/builders/staging/Linux%20linux_fuchsia_tests?limit=200
Fuchsia builder is green now, the disabled test is actively investigated
by @caroqliu . We can move fuchsia back to prod to avoid unexpected
breakages.

Author: zijiehe-google-com

engine/src/flutter/.ci.yaml

@@ -162,7 +162,6 @@ targets:
 
   - name: Linux linux_fuchsia_tests
     recipe: engine_v2/engine_v2
-    bringup: true
     timeout: 90
     enabled_branches:
       # Don't run this on release branches