Remove tool_host_cross_arch_tests bringup (#112311)

Author: jmagman

.ci.yaml

@@ -2843,7 +2843,6 @@ targets:
       - .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:
@@ -2864,7 +2863,6 @@ targets:
       - .ci.yaml
 
   - name: Mac_arm64 tool_host_cross_arch_tests
-    bringup: true # Mac_arm64 variant https://github.com/flutter/flutter/pull/109889
     recipe: flutter/flutter_drone
     timeout: 60
     properties: