Remove x64 "tool_host_cross_arch_tests" bringup (#112411)

.ci.yaml

diff --git a/.ci.yaml b/.ci.yaml
index 591cba6..69d827b 100644
--- a/.ci.yaml
+++ b/.ci.yaml
@@ -2843,7 +2843,6 @@
       - .ci.yaml
 
   - name: Mac_x64 tool_host_cross_arch_tests
-    bringup: true # Mac_x64 variant https://github.com/flutter/flutter/pull/109889
     recipe: flutter/flutter_drone
     timeout: 60
     properties: