[fuchsia/fuchsia] Don't pass `recipe` property to subbuild.

This would override the subbuild's recipe to fuchsia/fuchsia instead of
fuchsia/build.

Bug: 42426
Change-Id: Ie280098b8c9b0d9e32721318cdef8f3dc80eca51
diff --git a/recipes/fuchsia/fuchsia.expected/successful_build_and_test.json b/recipes/fuchsia/fuchsia.expected/successful_build_and_test.json
index f491b26..b09c124 100644
--- a/recipes/fuchsia/fuchsia.expected/successful_build_and_test.json
+++ b/recipes/fuchsia/fuchsia.expected/successful_build_and_test.json
@@ -159,7 +159,7 @@
     ],
     "infra_step": true,
     "name": "build.schedule",
-    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"bucket\": \"ci\", \"builder\": \"builder-subbuild\", \"project\": \"fuchsia\"}, \"experimental\": \"NO\", \"fields\": \"builder,createTime,createdBy,critical,endTime,id,input,number,output,startTime,status,updateTime\", \"gitilesCommit\": {\"host\": \"fuchsia.googlesource.com\", \"id\": \"2d72510e447ab60a9728aeea2362d8be2cbd7789\", \"project\": \"fuchsia\", \"ref\": \"refs/heads/master\"}, \"properties\": {\"$recipe_engine/source_manifest\": {\"debug_dir\": null}, \"experimental\": true, \"gcs_bucket\": \"###fuchsia-build###\", \"manifest\": \"manifest/minimal\", \"packages\": [\"//bundles/buildbot:core\"], \"parent_id\": \"8945511751514863184\", \"project\": \"integration\", \"recipe\": \"fuchsia/fuchsia\", \"remote\": \"https://fuchsia.googlesource.com/integration\", \"spec_revision\": \"deadbeef\", \"target\": \"x64\"}, \"requestId\": \"8945511751514863184-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
+    "stdin": "{\"requests\": [{\"scheduleBuild\": {\"builder\": {\"bucket\": \"ci\", \"builder\": \"builder-subbuild\", \"project\": \"fuchsia\"}, \"experimental\": \"NO\", \"fields\": \"builder,createTime,createdBy,critical,endTime,id,input,number,output,startTime,status,updateTime\", \"gitilesCommit\": {\"host\": \"fuchsia.googlesource.com\", \"id\": \"2d72510e447ab60a9728aeea2362d8be2cbd7789\", \"project\": \"fuchsia\", \"ref\": \"refs/heads/master\"}, \"properties\": {\"$recipe_engine/source_manifest\": {\"debug_dir\": null}, \"experimental\": true, \"gcs_bucket\": \"###fuchsia-build###\", \"manifest\": \"manifest/minimal\", \"packages\": [\"//bundles/buildbot:core\"], \"parent_id\": \"8945511751514863184\", \"project\": \"integration\", \"remote\": \"https://fuchsia.googlesource.com/integration\", \"spec_revision\": \"deadbeef\", \"target\": \"x64\"}, \"requestId\": \"8945511751514863184-00000000-0000-0000-0000-000000001337\", \"swarming\": {\"parentRunId\": \"fake-task-id\"}, \"tags\": [{\"key\": \"user_agent\", \"value\": \"recipe\"}]}}]}",
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ -201,7 +201,6 @@
       "@@@STEP_LOG_LINE@request@          ], @@@",
       "@@@STEP_LOG_LINE@request@          \"parent_id\": \"8945511751514863184\", @@@",
       "@@@STEP_LOG_LINE@request@          \"project\": \"integration\", @@@",
-      "@@@STEP_LOG_LINE@request@          \"recipe\": \"fuchsia/fuchsia\", @@@",
       "@@@STEP_LOG_LINE@request@          \"remote\": \"https://fuchsia.googlesource.com/integration\", @@@",
       "@@@STEP_LOG_LINE@request@          \"spec_revision\": \"deadbeef\", @@@",
       "@@@STEP_LOG_LINE@request@          \"target\": \"x64\"@@@",
diff --git a/recipes/fuchsia/fuchsia.py b/recipes/fuchsia/fuchsia.py
index 31b7243..df9c4a1 100644
--- a/recipes/fuchsia/fuchsia.py
+++ b/recipes/fuchsia/fuchsia.py
@@ -183,11 +183,12 @@
     parent_properties = api.properties.thaw()
     # These are reserved by kitchen and swarming. See
     # https://chromium.googlesource.com/infra/infra/+/2c2389a00fcdb93d90a628f941814f2abd34428e/go/src/infra/tools/kitchen/cook.go#266
-    # and https://chromium.googlesource.com/infra/infra/+/7fcd559afa7a866a5ad039019e6ef6a91922e09c/appengine/cr-buildbucket/validation.py#36
+    # and https://chromium.googlesource.com/infra/infra/+/7fcd559afa7a866a5ad039019e6ef6a91922e09c/appengine/cr-buildbucket/validation.py#36.
+    # We also should not override the 'recipe' of the child builder.
     reject_keys = {
         '$recipe_engine/path', '$recipe_engine/step', 'bot_id', 'path_config',
         'buildbucket', '$recipe_engine/buildbucket', 'buildername', 'branch',
-        'repository', '$recipe_engine/runtime'
+        'repository', '$recipe_engine/runtime', 'recipe'
     }
     properties = {
         key: val