[NFC] Link out to Swift.org for release branch PR directions

In an effort to centralize the release branch PR form and release
process info in general, remove any instances of such content and
link out to the dedicated section on Swift.org instead.

CONTRIBUTING.md

@@ -133,31 +133,7 @@ Once you've pushed your branch, you should see an option on this repository's pa
 
 ## Opening a PR for Release Branch
 
-In order for a pull request to be considered for inclusion in a release branch (e.g. `release/6.0`) after it has been cut, it must meet the following requirements:
-
-1. The title of the PR should start with the tag `[{swift version number}]`. For example, `[6.0]` for the Swift 6.0 release branch.
-
-1. The PR description must include the following information:
-
-    ```md
-    * **Explanation**: A description of the issue being fixed or enhancement being made. This can be brief, but it should be clear.
-    * **Scope**: An assessment of the impact/importance of the change. For example, is the change a source-breaking language change, etc.
-    * **Issue**: The GitHub Issue link if the change fixes/implements an issue/enhancement.
-    * **Original PR**: Pull Request link from the `main` branch.
-    * **Risk**: What is the (specific) risk to the release for taking this change?
-    * **Testing**: What specific testing has been done or needs to be done to further validate any impact of this change?
-    * **Reviewer**: One or more code owners for the impacted components should review the change. Technical review can be delegated by a code owner or otherwise requested as deemed appropriate or useful.
-    ```
-
-> [!TIP]
-> The PR description can be generated using the [release_branch.md](https://github.com/apple/sourcekit-lsp/blob/main/.github/PULL_REQUEST_TEMPLATE/release_branch.md) [pull request template](https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/about-issue-and-pull-request-templates). To use this template when creating a PR, you need to add the query parameter:
-> ```
-> ?expand=1&template=release_branch.md
-> ```
-> to the PR URL, as described in the [GitHub documentation on using query parameters to create a pull request](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/using-query-parameters-to-create-a-pull-request).
-> This is necessary because GitHub does not currently provide a UI to choose a PR template.
-
-All changes going into a release branch must go through pull requests that are approved and merged by the corresponding release manager.
+See our [directions](https://www.swift.org/contributing#release-branch-pull-requests) on how to propose a change for inclusion in a release branch.
 
 ## Review and CI Testing