Revert CONTRIBUTING.md change from D101685100

Summary:
Q&A request:

https://fb.workplace.com/groups/osssupport/permalink/31569486946006519/

D101685100 (a difftrain import for facebookresearch/tensor-layouts) unintentionally modified the standard fbcode/github/standard/CONTRIBUTING.md by adding a project-specific "Test layout" section. D102823690 attempted to revert the entire diff but cannot land because it needs export review. This diff reverts only the CONTRIBUTING.md change.

Followed previous example: D98217804

bypass-github-export-checks because people are requiring it but not running their diff trains.
diff-train-skip-merge  to unblock failing difftrain autosyncs from composer_model_library

___

overriding_review_checks_triggers_an_audit_and_retroactive_review
Oncall Short Name: triton

Differential Revision: D102848202

fbshipit-source-id: 8a4930135bb1799e56191c15e27181b2311f72ad

Author: FindHao

CONTRIBUTING.md

@@ -15,15 +15,6 @@ Note: pull requests are not imported into the GitHub directory in the usual way.
 5. Make sure your code lints.
 6. If you haven't already, complete the Contributor License Agreement ("CLA").
 
-## Test layout
-
-Test modules under `tests/` are named after the source module they cover
-(e.g. `tests/layouts.py` covers `src/tensor_layouts/layouts.py`). Pytest
-is configured to discover **every** `*.py` file in `tests/`, so anything
-added there must be either a test module or pytest infrastructure
-(`conftest.py`). Shared helpers belong in the source tree or in a
-`tests/_support/` module that pytest does not auto-collect.
-
 ## Contributor License Agreement ("CLA")
 In order to accept your pull request, we need you to submit a CLA. You only need
 to do this once to work on any of Meta's open source projects.