Remove "bringup: true" from "Linux Fuchsia FEMU" (#39651)

The emulator flakes appear to have been addressed.

There is a still a test flaking like here https://ci.chromium.org/ui/p/flutter/builders/staging/Linux%20Fuchsia%20FEMU/532/overview, but it is at a much lower rate, and from chat, I think it will soon be fixed by an upcoming Fuchsia SDK roll.

Author: zanderso

.ci.yaml

@@ -147,7 +147,6 @@ targets:
 
   - name: Linux Fuchsia FEMU
     recipe: engine/femu_test
-    bringup: true
     properties:
       add_recipes_cq: "true"
       build_fuchsia: "true"