CircleCI: Remove test_codegen (#34733)

Summary:
The CircleCI `test_codegen` job currently runs tests under `packages/react-native-codegen`. Because it runs from that working directory, it doesn't pick up the project root's `jest.config.js`, which is a problem for https://github.com/facebook/react-native/pull/34724 (snapshot format configuration in `jest.config.js`)

`react-native-codegen` tests are *already run* by the `test_js` job, as can be seen from the CircleCI logs
https://app.circleci.com/pipelines/github/facebook/react-native/15818/workflows/41034d00-7061-46e8-a03d-abdcc7fd7e2f/jobs/295804/parallel-runs/0/steps/0-107 , so the job isn't necessary, and this PR removes it. CC cipolleschi

## Changelog

[Internal] [Fixed] - Remove redundant `test_codegen` job from CircleCI.

Pull Request resolved: https://github.com/facebook/react-native/pull/34733

Test Plan: CircleCI!

Reviewed By: lunaleaps

Differential Revision: D39660829

Pulled By: robhogan

fbshipit-source-id: d7b09cc90a30e7604e2645e2bd0c16f840443153

.circleci/config.yml

@@ -403,27 +403,6 @@ jobs:
       - store_test_results:
           path: ./reports/junit
 
-  # -----------------------
-  #     JOBS: Codegen Tests
-  # -----------------------
-  test_codegen:
-    parameters:
-      executor:
-        type: executor
-        default: nodelts
-    executor: << parameters.executor >>
-    steps:
-      - checkout
-      - setup_artifacts
-      - run:
-          name: Install Yarn in codegen
-          command: yarn install
-          working_directory: packages/react-native-codegen
-      - run:
-          name: Run Tests
-          command: yarn jest
-          working_directory: packages/react-native-codegen
-
   # -------------------------
   #     JOBS: iOS Unit Tests
   # -------------------------
@@ -1361,7 +1340,6 @@ workflows:
     unless: << pipeline.parameters.run_package_release_workflow_only >>
     jobs:
       - prepare_hermes_workspace
-      - test_codegen
       - build_hermesc_linux:
           requires:
             - prepare_hermes_workspace