chore: remove unused git-cliff configuration (#31066)

## Why

`cliff.toml` was originally used by the TypeScript CLI release tooling
to generate the changelog. #2048 removed that tooling, including the
`git-cliff` dependency and changelog package script, but left the
configuration behind. #2780 subsequently replaced the generated
`CHANGELOG.md` contents with a link to GitHub Releases, and the current
Rust release workflow builds release notes from the tagged commit
message.

Nothing in the repository references `cliff.toml` or `git-cliff`
anymore, so retaining the file misleadingly suggests that it is part of
the supported release process.

## What changed

- Delete the unused root-level `cliff.toml` configuration.

## Testing

Not run (non-executable configuration cleanup only).

cliff.toml

@@ -1,46 +0,0 @@
-# https://git-cliff.org/docs/configuration
-
-[changelog]
-header = """
-# Changelog
-
-You can install any of these versions: `npm install -g @openai/codex@<version>`
-"""
-
-body = """
-{% if version -%}
-## [{{ version | trim_start_matches(pat="v") }}] - {{ timestamp | date(format="%Y-%m-%d") }}
-{%- else %}
-## [unreleased]
-{% endif %}
-
-{%- for group, commits in commits | group_by(attribute="group") %}
-### {{ group | striptags | trim }}
-
-{% for commit in commits %}- {% if commit.scope %}*({{ commit.scope }})* {% endif %}{% if commit.breaking %}[**breaking**] {% endif %}{{ commit.message | upper_first }}
-{% endfor %}
-
-{%- endfor -%}
-"""
-
-footer = """
-<!-- generated - do not edit -->
-"""
-
-trim = true
-postprocessors = []
-
-[git]
-conventional_commits = true
-
-commit_parsers = [
-  { message = "^feat", group = "<!-- 0 -->🚀 Features" },
-  { message = "^fix",  group = "<!-- 1 -->🪲 Bug Fixes" },
-  { message = "^bump", group = "<!-- 6 -->🛳️ Release" },
-  # Fallback – skip anything that didn't match the above rules.
-  { message = ".*",  group = "<!-- 10 -->💼 Other" },
-]
-
-filter_unconventional = false
-sort_commits = "oldest"
-topo_order = false