Remove release vector repos to require CONTRIBUTING.md. (#159)

Author: Gerrit91

docs/contributing/04-release-flow.md

@@ -61,13 +61,6 @@ Before adding a repository in the metal-stack org to the releases repository, it
     - The team should contain at least two maintainers.
   - `LICENSE`
     - This usually should be MIT with "metal-stack" as authors.
-  - `CONTRIBUTING.md`
-    - This should contain the following content:
-      ```
-      # Contributing
-
-      Please check out the [contributing section](https://docs.metal-stack.io/stable/development/contributing/) in our [docs](https://docs.metal-stack.io/).
-      ```
   - `README.md`
 - The `developers-core` team should be given repository access with `write` role, the codeowners team should have the `maintain` role
 - Release artifacts should have an SPDX-formatted SBOM attached.