bin: Remove obsolete bin/setup-local-env.sh

The script was retired ~7 years ago in #17004 when the project moved to
the Core local environment (wp-env). Since then it only printed a notice
telling users it had been retired. Nothing in the codebase references it,
so the stub can be safely removed.

Author: manzoorwanijk

PR_DESCRIPTION.md

@@ -0,0 +1,31 @@
+## What?
+
+Removes the obsolete `bin/setup-local-env.sh` script.
+
+## Why?
+
+This script was retired roughly 7 years ago in [#17004](https://github.com/WordPress/gutenberg/pull/17004) ("Switch to using the Core local environment"), when the project moved to `wp-env` / the Core local environment. Since then its only content has been a notice telling users it has been retired and to run `npm run wp-env start` instead.
+
+Nothing in the codebase references the script anymore (no `package.json` scripts, docs, or other tooling point to it), so the stub serves no purpose and can be safely removed.
+
+## How?
+
+Deletes `bin/setup-local-env.sh`. No other files reference it, so no further changes are needed.
+
+## Testing Instructions
+
+1. Confirm `bin/setup-local-env.sh` no longer exists.
+2. Run `git grep setup-local-env` and verify there are no remaining references.
+3. Verify the documented local-environment workflow is unaffected: `npm run wp-env start` still sets up a local environment as expected.
+
+### Testing Instructions for Keyboard
+
+N/A — no user interface changes.
+
+## Screenshots or screencast
+
+N/A
+
+## Use of AI Tools
+
+This pull request was authored with the assistance of Claude Code. All changes were reviewed by the author.