Revert #154339, remove bringup on linux customer testing (#154372)

Reverts increased timeouts on customer testing from #154339, also removes bringup state from https://github.com/flutter/flutter/issues/154293.
This was related to https://github.com/flutter/flutter/issues/154251, which will be fixed by https://github.com/flutter/tests/pull/406 (so we should land that first).

.ci.yaml

@@ -533,8 +533,6 @@ targets:
       - .ci.yaml
 
   - name: Linux customer_testing
-    # TODO(Piinks): https://github.com/flutter/flutter/issues/154251
-    bringup: true
     # This really just runs dev/bots/customer_testing/ci.sh,
     # but it does so indirectly via the flutter_drone recipe
     # calling the dev/bots/test.dart script.
@@ -547,8 +545,6 @@ targets:
       shard: customer_testing
       tags: >
         ["framework", "hostonly", "shard", "linux"]
-      # Timeout in seconds for each individual step.
-      test_timeout_secs: "2700" # 45 minutes * 60
 
   - name: Linux docs_publish
     recipe: flutter/docs
@@ -3751,8 +3747,6 @@ targets:
       shard: customer_testing
       tags: >
         ["framework", "hostonly", "shard", "mac"]
-      # Timeout in seconds for each individual step.
-      test_timeout_secs: "2700" # 45 minutes * 60
 
   - name: Mac dart_plugin_registry_test
     recipe: devicelab/devicelab_drone
@@ -5421,8 +5415,6 @@ targets:
       shard: customer_testing
       tags: >
         ["framework", "hostonly", "shard", "windows"]
-      # Timeout in seconds for each individual step.
-      test_timeout_secs: "2700" # 45 minutes * 60
 
   - name: Windows framework_tests_libraries
     recipe: flutter/flutter_drone