Remove the generated changelog PR from the publish workflow

[fabriziocucci]

Summary:

Removes the generate_changelog job from the publish workflow, along with generate-changelog.yml, generateChangelog.js and its test.

The job opened a changelog/v<version> PR with every section present, empty or not, an Unknown bucket and the release machinery's own commits in it. Every one was then curated by hand. The release copilot (reactwg/react-native-releases#1425) now opens that PR itself. It runs the same @rnx-kit/rn-changelog-generator against the same base, drops the machinery commits, sorts by scope and omits empty sections. It also opens the .0 consolidation, which the job always skipped (0.88's was #59122, done by hand).

create_draft_release listed generate_changelog in needs and its if. It depended on it for ordering only: createDraftRelease.js runs git checkout -b changelog/v<version>, which creates a new local branch from the tag and never reads the bot's branch. The tag's own CHANGELOG.md never carries the release's section (checked for v0.88.0-rc.4, v0.88.0-rc.6 and v0.87.1), which is why the draft notes have always come out empty. It now depends on publish_react_native directly, so it still runs only after a successful publish.

The publish workflow runs from the tag's branch, so this takes effect from the first branch cut after it lands. Existing *-stable branches keep the job unless this is picked. The copilot defers to the bot wherever the job is still present, so the two never open the same branch.

This should land after reactwg/react-native-releases#1425, since that is where the replacement lives.

Changelog:

[INTERNAL] [REMOVED] - Remove the generated changelog PR from the publish workflow

Test Plan:

• yarn jest .github/workflow-scripts: 10 suites, 61 tests pass.
• Every file in .github/workflows parses as YAML. In publish-npm.yml, every needs entry names an existing job and nothing references generate_changelog.
• git grep for generate_changelog, generate-changelog and generateChangelog finds nothing under .github after the change.
• The replacement was exercised as a dry run against v0.88.0-rc.6: it ran the generator, resolved the commits and pushed nothing.